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+<html>
+ <head>
+ <title>
+ HDF5 File Format Specification Version 1.1
+ </title>
+
+<STYLE TYPE="text/css">
+
+P { text-indent: 2em}
+P.item { margin-left: 2em; text-indent: -2em}
+P.item2 { margin-left: 2em; text-indent: 2em}
+
+TABLE.format { border:solid; border-collapse:collapse; caption-side:top; text-align:center; width:80%;}
+TABLE.format TH { border:ridge; padding:4px; width:25%;}
+TABLE.format TD { border:ridge; padding:4px; }
+TABLE.format CAPTION { font-weight:bold; font-size:larger;}
+
+TABLE.note {border:none; text-align:right; width:80%;}
+
+TABLE.desc { border:solid; border-collapse:collapse; caption-size:top; text-align:left; width:80%;}
+TABLE.desc TR { vertical-align:top;}
+TABLE.desc TH { border-style:ridge; font-size:larger; padding:4px; text-decoration:underline;}
+TABLE.desc TD { border-style:ridge; padding:4px; }
+TABLE.desc CAPTION { font-weight:bold; font-size:larger;}
+
+TABLE.list { border:none; }
+TABLE.list TR { vertical-align:top;}
+TABLE.list TH { border:none; text-decoration:underline;}
+TABLE.list TD { border:none; }
+
+</STYLE>
+</head>
+ <body>
+
+ <center>
+ <table border=0 width=90%>
+ <tr>
+ <td valign=top>
+ <ol type=I>
+ <li><a href="#Intro">Introduction</a>
+ <li><a href="#FileMetaData">Disk Format Level 0 - File Metadata</a>
+ <font size=-2>
+ <ol type=A>
+ <li><a href="#SuperBlock">Disk Format Level 0A - File Signature and Super Block</a>
+ <li><a href="#DriverInfo">Disk Format Level 0B - File Driver Info</a>
+ </ol>
+ </font>
+ <li><a href="#FileInfra">Disk Format Level 1 - File Infrastructure</a>
+ <font size=-2>
+ <ol type=A>
+ <li><a href="#Btrees">Disk Format Level 1A - B-link Trees and B-tree Nodes</a>
+ <li><a href="#SymbolTable">Disk Format Level 1B - Group</a>
+ <li><a href="#SymbolTableEntry">Disk Format Level 1C - Group Entry</a>
+ <li><a href="#LocalHeap">Disk Format Level 1D - Local Heaps</a>
+ <li><a href="#GlobalHeap">Disk Format Level 1E - Global Heap</a>
+ <li><a href="#FreeSpaceIndex">Disk Format Level 1F - Free-space Index</a>
+ </ol>
+ </font>
+ <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a>
+ <font size=-2>
+ <ol type=A>
+ <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a>
+ <ol type=1>
+ <li><a href="#NILMessage">Name: NIL</a> <!-- 0x0000 -->
+ <li><a href="#SimpleDataSpace">Name: Simple Dataspace</a> <!-- 0x0001 -->
+<!-- <li><a href="#DataSpaceMessage">Name: Complex Dataspace</a> --> <!-- 0x0002 -->
+ <li><a href="#ReservedMessage_0002">Name: Reserved - not assigned yet</a> <!-- 0x0002 -->
+ <li><a href="#DataTypeMessage">Name: Datatype</a> <!-- 0x0003 -->
+ <li><a href="#OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a> <!-- 0x0004 -->
+ <li><a href="#FillValueMessage">Name: Data Storage - Fill Value</a> <!-- 0x0005 -->
+ </ol>
+ </ol>
+ </font>
+ </ol>
+ </td><td>&nbsp;&nbsp;</td><td valign=top>
+ <ol type=I start=4>
+
+ <li><a href="#DataObject">Disk Format Level 2 - Data Objects</a>
+ <font size=-2><i>(Continued)</i>
+ <ol type=A>
+ <li><a href="#ObjectHeader">Disk Format Level 2a - Data Object Headers</a><i>(Continued)</i>
+ <ol type=1 start=6>
+<!-- <li><a href="#CompactDataStorageMessage">Name: Data Storage - Compact</a> --> <!-- 0x0006 -->
+ <li><a href="#ReservedMessage_0006">Name: Reserved - not assigned yet</a> <!-- 0x0006 -->
+ <li><a href="#ExternalFileListMessage">Name: Data Storage - External Data Files</a> <!-- 0x0007 -->
+ <li><a href="#LayoutMessage">Name: Data Storage - Layout</a> <!-- 0x0008 -->
+ <li><a href="#ReservedMessage_0009">Name: Reserved - not assigned yet</a> <!-- 0x0009 -->
+ <li><a href="#ReservedMessage_000A">Name: Reserved - not assigned yet</a> <!-- 0x000a -->
+ <li><a href="#FilterMessage">Name: Data Storage - Filter Pipeline</a> <!-- 0x000b -->
+ <li><a href="#AttributeMessage">Name: Attribute</a> <!-- 0x000c -->
+ <li><a href="#CommentMessage">Name: Object Comment</a> <!-- 0x000d -->
+ <li><a href="#OldModifiedMessage">Name: Object Modification Date and Time (Old)</a> <!-- 0x000e -->
+ <li><a href="#SharedMessage">Name: Shared Object Message</a> <!-- 0x000f -->
+ <li><a href="#ContinuationMessage">Name: Object Header Continuation</a> <!-- 0x0010 -->
+ <li><a href="#SymbolTableMessage">Name: Group Message</a> <!-- 0x0011 -->
+ <li><a href="#ModifiedMessage">Name: Object Modification Date and Time</a> <!-- 0x0012 -->
+ </ol>
+ <li><a href="#DataStorage">Disk Format: Level 2b - Data Object Data Storage</a>
+ </ol>
+ </font>
+ <LI><A href="#Appendix">Appendix</A>
+ </ol>
+</td></tr>
+</table>
+</center>
+
+ <BR>
+ <HR>
+
+
+ <h2>Introduction</h2>
+
+ <table align=right width=100>
+ <tr><td>&nbsp;</td><td align=center>
+ <hr>
+ <img src="FF-IH_FileGroup.gif" alt="HDF5 Groups" hspace=15 vspace=15>
+ </td><td>&nbsp;</td></tr>
+ <tr><td>&nbsp;</td><td align=center>
+ <strong>Figure 1:</strong> Relationships among the HDF5 root group, other groups, and objects
+ <hr>
+ </td><td>&nbsp;</td></tr>
+
+ <tr><td>&nbsp;</td><td align=center>
+ <img src="FF-IH_FileObject.gif" alt="HDF5 Objects" hspace=15 vspace=15>
+ </td><td>&nbsp;</td></tr>
+ <tr><td>&nbsp;</td><td align=center>
+ <strong>Figure 2:</strong> HDF5 objects -- datasets, datatypes, or dataspaces
+ <hr>
+ </td><td>&nbsp;</td></tr>
+ </table>
+
+
+ <P>The format of an HDF5 file on disk encompasses several
+ key ideas of the HDF4 and AIO file formats as well as
+ addressing some shortcomings therein. The new format is
+ more self-describing than the HDF4 format and is more
+ uniformly applied to data objects in the file.
+
+ <P>An HDF5 file appears to the user as a directed graph.
+ The nodes of this graph are the higher-level HDF5 objects
+ that are exposed by the HDF5 APIs:
+
+ <ul>
+ <li>Groups
+ <li>Datasets
+ <li>Named datatypes
+ </ul>
+
+ <P>At the lowest level, as information is actually written to the disk,
+ an HDF5 file is made up of the following objects:
+ <ul>
+ <li>A super block
+ <li>B-tree nodes (containing either symbol nodes or raw data chunks)
+ <li>Object headers
+ <li>A global heap
+ <li>Local heaps
+ <li>Free space
+ </ul>
+
+ <P>The HDF5 library uses these low-level objects to represent the
+ higher-level objects that are then presented to the user or
+ to applications through the APIs.
+ For instance, a group is an object header that contains a message that
+ points to a local heap and to a B-tree which points to symbol nodes.
+ A dataset is an object header that contains messages that describe
+ datatype, space, layout, filters, external files, fill value, etc
+ with the layout message pointing to either a raw data chunk or to a
+ B-tree that points to raw data chunks.
+
+
+ <h3>This Document</h3>
+
+ <p>This document describes the lower-level data objects;
+ the higher-level objects and their properties are described
+ in the <a href="H5.user.html"><cite>HDF5 User's Guide</cite></a>.
+
+ <P>Three levels of information comprise the file format.
+ Level 0 contains basic information for identifying and
+ defining information about the file. Level 1 information contains
+ the information about the pieces of a file shared by many objects
+ in the file (such as a B-trees and heaps). Level 2 is the rest
+ of the file and contains all of the data objects, with each object
+ partitioned into header information, also known as
+ <em>metadata</em>, and data.
+
+ <p>The sizes of various fields in the following layout tables are
+ determined by looking at the number of columns the field spans
+ in the table. There are three exceptions: (1) The size may be
+ overridden by specifying a size in parentheses, (2) the size of
+ addresses is determined by the <em>Size of Offsets</em> field
+ in the super block and is indicated in this document with a
+ superscripted 'O', and (3) the size of length fields is determined
+ by the <em>Size of Lengths</em> field in the super block and is
+ indicated in this document with a superscripted 'L'.
+
+ <P>Values for all fields in this document should be treated as unsigned
+ integers, unless otherwise noted in the description of a field.
+ Additionally, all metadata fields are stored in little-endian byte
+ order.
+ </P>
+
+ <BR>
+ <HR>
+
+ <h2><a name="FileMetaData">
+ Disk Format: Level 0 - File Metadata</a></h2>
+
+ <H3><A name="SuperBlock">
+ Disk Format: Level 0A - File Signature and Super Block</A></H3>
+
+ <P>The super block may begin at certain predefined offsets within
+ the HDF5 file, allowing a block of unspecified content for
+ users to place additional information at the beginning (and
+ end) of the HDF5 file without limiting the HDF5 library's
+ ability to manage the objects within the file itself. This
+ feature was designed to accommodate wrapping an HDF5 file in
+ another file format or adding descriptive information to the
+ file without requiring the modification of the actual file's
+ information. The super block is located by searching for the
+ HDF5 file signature at byte offset 0, byte offset 512 and at
+ successive locations in the file, each a multiple of two of
+ the previous location, i.e. 0, 512, 1024, 2048, etc.
+
+ <P>The super block is composed of a file signature, followed by
+ super block and group version numbers, information
+ about the sizes of offset and length values used to describe
+ items within the file, the size of each group page,
+ and a group entry for the root object in the file.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ HDF5 Super Block Layout
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>HDF5 File Signature (8 bytes)<br><br></td>
+ </tr>
+
+ <tr>
+ <td>Version # of Super Block</td>
+ <td>Version # of Global Free-space Storage</td>
+ <td>Version # of Root Group Symbol Table Entry</td>
+ <td>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td>Version # of Shared Header Message Format</td>
+ <td>Size of Offsets</td>
+ <td>Size of Lengths</td>
+ <td>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Group Leaf Node K</td>
+ <td colspan=2>Group Internal Node K</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>File Consistency Flags</td>
+ </tr>
+
+ <tr>
+ <td colspan=2 style="border:dotted;">Indexed Storage Internal Node K<sup>1</sup></td>
+ <td colspan=2 style="border:dotted;">Reserved (zero)<sup>1</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Base Address<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Address of Global Free-space Heap<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>End of File Address<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Driver Information Block Address<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Root Group Symbol Table Entry</td>
+ </tr>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'O' the above table are
+ <br>
+ of the size specified in "Size of Offsets.")
+ </td></tr>
+ <tr><td>
+ (Items marked with an '1' the above table are
+ <br>
+ new in version 1 of the superblock)
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>HDF5 File Signature</td>
+ <td>
+ <P>This field contains a constant value and can be used to
+ quickly identify a file as being an HDF5 file. The
+ constant value is designed to allow easy identification of
+ an HDF5 file and to allow certain types of data corruption
+ to be detected. The file signature of an HDF5 file always
+ contains the following values:
+ </P>
+
+ <center>
+ <table border align=center cellpadding=4>
+ <tr align=center>
+ <td align=right>Decimal:</td>
+ <td width="8%">137</td>
+ <td width="8%">72</td>
+ <td width="8%">68</td>
+ <td width="8%">70</td>
+ <td width="8%">13</td>
+ <td width="8%">10</td>
+ <td width="8%">26</td>
+ <td width="8%">10</td>
+ </tr>
+
+ <tr align=center>
+ <td align=right>Hexadecimal:</td>
+ <td>89</td>
+ <td>48</td>
+ <td>44</td>
+ <td>46</td>
+ <td>0d</td>
+ <td>0a</td>
+ <td>1a</td>
+ <td>0a</td>
+ </tr>
+
+ <tr align=center>
+ <td align=right>ASCII C Notation:</td>
+ <td>\211</td>
+ <td>H</td>
+ <td>D</td>
+ <td>F</td>
+ <td>\r</td>
+ <td>\n</td>
+ <td>\032</td>
+ <td>\n</td>
+ </tr>
+ </table>
+ </center>
+ <br>
+
+ <P>This signature both identifies the file as an HDF5 file
+ and provides for immediate detection of common
+ file-transfer problems. The first two bytes distinguish
+ HDF5 files on systems that expect the first two bytes to
+ identify the file type uniquely. The first byte is
+ chosen as a non-ASCII value to reduce the probability
+ that a text file may be misrecognized as an HDF5 file;
+ also, it catches bad file transfers that clear bit
+ 7. Bytes two through four name the format. The CR-LF
+ sequence catches bad file transfers that alter newline
+ sequences. The control-Z character stops file display
+ under MS-DOS. The final line feed checks for the inverse
+ of the CR-LF translation problem. (This is a direct
+ descendent of the <A href="http://www.libpng.org/pub/png/spec/PNG-Rationale.html#R.PNG-file-signature">PNG</A> file
+ signature.)
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version Number of the Super Block</td>
+ <td>
+ <P>This value is used to determine the format of the
+ information in the super block. When the format of the
+ information in the super block is changed, the version number
+ is incremented to the next integer and can be used to
+ determine how the information in the super block is
+ formatted.
+ </P>
+
+ <P>Values of 0 and 1 are defined for this field.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version Number of the File Free-space Information</td>
+ <td>
+ <P>This value is used to determine the format of the
+ information in the File Free-space Information.
+ </P>
+ <P>The only value currently valid in this field is '0', which
+ indicates that the free space index is formatted as described
+ <A href="#FreeSpaceIndex">below</A>.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version Number of the Root Group Symbol Table Entry</td>
+ <td>
+ <P>This value is used to determine the format of the
+ information in the Root Group Symbol Table Entry. When the
+ format of the information in that field is changed, the
+ version number is incremented to the next integer and can be
+ used to determine how the information in the field
+ is formatted.
+ </P>
+ <P>The only value currently valid in this field is '0', which
+ indicates that the root group symbol table entry is formatted as
+ described <A href="#SymbolTableEntry">below</A>.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version Number of the Shared Header Message Format</td>
+ <td>
+ <P>This value is used to determine the format of the
+ information in a shared object header message. Since the format
+ of the shared header messages differs from the other private
+ header messages, a version number is used to identify changes
+ in the format.
+ </P>
+ <P>The only value currently valid in this field is '0', which
+ indicates that shared header messages are formatted as
+ described <A href="#SharedMessage">below</A>.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size of Offsets</td>
+ <td>
+ <P>This value contains the number of bytes used to store
+ addresses in the file. The values for the addresses of
+ objects in the file are offsets relative to a base address,
+ usually the address of the super block signature. This
+ allows a wrapper to be added after the file is created
+ without invalidating the internal offset locations.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size of Lengths</td>
+ <td>
+ <P>This value contains the number of bytes used to store
+ the size of an object.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Group Leaf Node K</td>
+ <td>
+ <P>Each leaf node of a group B-tree will have at
+ least this many entries but not more than twice this
+ many. If a group has a single leaf node then it
+ may have fewer entries.
+ </P>
+ <P>This value must be greater than zero.
+ </P>
+ <P>See the <A href="#Btrees">description</A> of B-trees below.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Group Internal Node K</td>
+ <td>
+ <P>Each internal node of a group B-tree will have at
+ least this many entries but not more than twice this
+ many. If the group has only one internal
+ node then it might have fewer entries.
+ </P>
+ <P>This value must be greater than zero.
+ </P>
+ <P>See the <A href="#Btrees">description</A> of B-trees below.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>File Consistency Flags</td>
+ <td>
+ <P>This value contains flags to indicate information
+ about the consistency of the information contained
+ within the file. Currently, the following bit flags are
+ defined:
+ <ul>
+ <li>Bit 0 set indicates that the file is opened for
+ write-access.
+ <li>Bit 1 set indicates that the file has
+ been verified for consistency and is guaranteed to be
+ consistent with the format defined in this document.
+ <li>Bits 2-31 are reserved for future use.
+ </ul>
+ Bit 0 should be
+ set as the first action when a file is opened for write
+ access and should be cleared only as the final action
+ when closing a file. Bit 1 should be cleared during
+ normal access to a file and only set after the file's
+ consistency is guaranteed by the library or a
+ consistency utility.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Indexed Storage Internal Node K</td>
+ <td>
+ <P>Each internal node of a indexed storage B-tree will have at
+ least this many entries but not more than twice this
+ many. If the group has only one internal
+ node then it might have fewer entries.
+ </P>
+ <P>This value must be greater than zero.
+ </P>
+ <P>See the <A href="#Btrees">description</A> of B-trees below.
+ </P>
+
+ <P><EM>This field is present in version 1+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Base Address</td>
+ <td>
+ <P>This is the absolute file address of the first byte of
+ the HDF5 data within the file. The library currently
+ constrains this value to be the absolute file address
+ of the super block itself when creating new files;
+ future versions of the library may provide greater
+ flexibility. When opening an existing file and this address does
+ not match the offset of the superblock, the library assumes
+ that the entire contents of the HDF5 file have been adjusted in
+ the file and adjusts the base address and end of file address to
+ reflect their new positions in the file. Unless otherwise noted,
+ all other file addresses are relative to this base
+ address.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Address of Global Free-space Index</td>
+ <td>
+ <P>Free-space management is not yet defined in the HDF5
+ file format and is not handled by the library.
+ Currently this field always contains the
+ <A href="#UndefinedAddress">undefined address</A>.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>End of File Address</td>
+ <td>
+ <P>This is the absolute file address of the first byte past
+ the end of all HDF5 data. It is used to determine whether a
+ file has been accidently truncated and as an address where
+ file data allocation can occur if space from the free list is
+ not used.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Driver Information Block Address</td>
+ <td>
+ <P>This is the relative file address of the file driver
+ information block which contains driver-specific
+ information needed to reopen the file. If there is no
+ driver information block then this entry should be the
+ <A href="#UndefinedAddress">undefined address</A>.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Root Group Symbol Table Entry</td>
+ <td>
+ <P>This is the <A href="#SymbolTableEntry">symbol table entry</A>
+ of the root group, which serves as the entry point into
+ the group graph for the file.
+ </P>
+
+ <P><EM>This field is present in version 0+ of the superblock.</EM>
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <H3><A name="DriverInfo">
+ Disk Format: Level 0B - File Driver Info</A></H3>
+
+ <p>The <em>file driver information block</em> is an optional region of the
+ file which contains information needed by the file driver in
+ order to reopen a file. The format of the file driver information
+ block is:
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Driver Information Block
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Driver Information Size (4 bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Driver Identification (8 bytes)<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br><br>Driver Information (<em>n</em> bytes)<br><br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>The version number of the driver information block. The
+ file format documented here is version zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Driver Information Size</td>
+ <td>
+ <P>The size in bytes of the Driver Information part of this
+ structure.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Driver Identification</td>
+ <td>
+ <P>This is an eight-byte ASCII string without null
+ termination which identifies the driver and version number
+ of the Driver Information block. The predefined drivers
+ supplied with the HDF5 library are identified by the
+ letters <code>NCSA</code> followed by the first four characters of
+ the driver name. If the Driver Information block is not
+ the original version then the last letter(s) of the
+ identification will be replaced by a version number in
+ ASCII.
+ </P>
+ <P>
+ For example, the various versions of the <em>multi driver</em>
+ will be identified by <code>NCSAmult</code>.
+ (<code>NCSAmult</code> is simply <code>NCSAmulti</code> truncated
+ to eight characters. Subsequent identifiers will be created by
+ substituting sequential numerical values for the final character,
+ starting with zero.) <em>multi driver</em> is the only default driver that
+ is encoded in this field.
+ </P>
+ <P>
+ Identification for user-defined drivers
+ is eight-byte long and arbitrary but should be unique and avoid
+ the four character prefix "NCSA".
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Driver Information</td>
+ <td>Driver information is encoded/decoded in a format defined by the
+ file driver. <em>multi driver</em> is the only default driver that has driver
+ information stored in this field. Its format is explained in the
+ following block.</td>
+ </tr>
+ </table>
+ </div>
+
+ <BR>
+ <P><em>Multi driver</em> has the following format:</P>
+
+ <div align=center>
+ <table class=format>
+ <caption>
+ Multi Driver Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Member Mapping</td>
+ <td>Member Mapping</td>
+ <td>Member Mapping</td>
+ <td>Member Mapping</td>
+ </tr>
+
+ <tr>
+ <td>Member Mapping</td>
+ <td>Member Mapping</td>
+ <td>Reserved</td>
+ <td>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Address of Member File 1<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>End of Address for Member File 1<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Address of Member File 2<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>End of Address for Member File 2<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>... ...<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name of Member File 1<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name of Member File 2<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>... ...<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Member Mapping</td>
+ <td><P><em>Multi driver</em> enables different types of HDF5 data and
+ metadata to be written to separate files. These files are viewed by the
+ library as a single virtual HDF5 file with a single file address.
+ It allows maximal 6 files to be created.
+ In sequence, these <em>Member Mapping</em> fields are for super block,
+ B-tree, raw data, global heap, local heap,
+ and object header. More than one type of data can be written to the
+ same file.</P>
+ <P>These <em>Member Mapping</em> fields are integer values from 1 to 6
+ indicating how the data can be mapped to or merged with another type of
+ data.
+ <table class=list>
+ <tr>
+ <th width="30%">Member Mapping</th>
+ <th align=left>Description</th>
+ </tr>
+ <tr>
+ <td align=center>1</td>
+ <td>The super block data.</td>
+ </tr>
+ <tr>
+ <td align=center>2</td>
+ <td>The B-tree data.</td>
+ </tr>
+ <tr>
+ <td align=center>3</td>
+ <td>The raw data.</td>
+ </tr>
+ <tr>
+ <td align=center>4</td>
+ <td>The global heap data.</td>
+ </tr>
+ <tr>
+ <td align=center>5</td>
+ <td>The local heap data.</td>
+ </tr>
+ <tr>
+ <td align=center>6</td>
+ <td>The object header data.</td>
+ </tr>
+ </table></P>
+ For example, if the third field has the value 3 and all the rest have the
+ value 1, it means there are two files, one for raw data, one for super block,
+ B-tree, global heap, local heap, and object header.
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td><P>These fields are reserved and should always be zero.</P></td>
+ </tr>
+
+ <tr>
+ <td>Address of Member File</td>
+ <td><P>Specifies the virtual address. A normally eight-byte integer with
+ the value from <em>0</em> (zero) to maximal value,
+ at which the member file starts.</P></td>
+ </tr>
+
+ <tr>
+ <td>End of Address for Member File</td>
+ <td><P>The end of allocated address for the member file. A normally eight-byte
+ integer value.</P></td>
+ </tr>
+
+ <tr>
+ <td>Name of Member File</td>
+ <td><P>The null-terminated name of member file. Its length should be multiples of
+ 8 bytes. Additional bytes will be padded with <em>NULL</em>s. The default naming
+ convention is <em>%%s-X.h5</em>, where <em>X</em> is one of the letters
+ <em>s</em> (for super block), <em>b</em> (for B-tree), <em>r</em> (for raw data),
+ <em>g</em> (for global heap), <em>l</em> (for local heap), and <em>o</em> (for
+ object header). The name for the whole HDF5 file will substitute the <em>%s</em>
+ in the string.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <BR>
+ <HR>
+
+ <h2><a name="FileInfra">
+ Disk Format: Level 1 - File Infrastructure</a></h2>
+ <h3><a name="Btrees">Disk Format: Level 1A - B-link Trees and B-tree Nodes</a></h3>
+
+ <p>B-link trees allow flexible storage for objects which tend to grow
+ in ways that cause the object to be stored discontiguously. B-trees
+ are described in various algorithms books including "Introduction to
+ Algorithms" by Thomas H. Cormen, Charles E. Leiserson, and Ronald
+ L. Rivest. The B-link tree, in which the sibling nodes at a
+ particular level in the tree are stored in a doubly-linked list,
+ is described in the "Efficient Locking for Concurrent Operations
+ on B-trees" paper by Phillip Lehman and S. Bing Yao as published
+ in the <cite>ACM Transactions on Database Systems</cite>, Vol. 6,
+ No. 4, December 1981.
+
+ <p>The B-link trees implemented by the file format contain one more
+ key than the number of children. In other words, each child
+ pointer out of a B-tree node has a left key and a right key.
+ The pointers out of internal nodes point to sub-trees while
+ the pointers out of leaf nodes point to symbol nodes and
+ raw data chunks.
+ Aside from that difference, internal nodes and leaf nodes
+ are identical.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ B-tree Nodes
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+
+ <tr>
+ <td colspan=4>Signature</td>
+
+ <tr>
+ <td>Node Type</td>
+ <td>Node Level</td>
+ <td colspan=2>Entries Used</td>
+
+ <tr>
+ <td colspan=4>Address of Left Sibling<sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>Address of Right Sibling<sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>Key 0 (variable size)</td>
+
+ <tr>
+ <td colspan=4>Address of Child 0<sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>Key 1 (variable size)</td>
+
+ <tr>
+ <td colspan=4>Address of Child 1<sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>...</td>
+
+ <tr>
+ <td colspan=4>Key 2<em>K</em> (variable size)</td>
+
+ <tr>
+ <td colspan=4>Address of Child 2<em>K</em><sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>Key 2<em>K</em>+1 (variable size)</td>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'O' the above table are
+ <br>
+ of the size specified in "Size of Offsets.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Signature</td>
+ <td>
+ <P>The ASCII character string "<code>TREE</code>" is
+ used to indicate the
+ beginning of a B-link tree node. This gives file
+ consistency checking utilities a better chance of
+ reconstructing a damaged file.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Node Type</td>
+ <td>
+ <P>Each B-link tree points to a particular type of data.
+ This field indicates the type of data as well as
+ implying the maximum degree <em>K</em> of the tree and
+ the size of each Key field.
+ </P>
+
+ <table class=list>
+ <tr>
+ <th width="30%">Node Type</th>
+ <th align=left>Description</th>
+ </tr>
+ <tr>
+ <td align=center>0</td>
+ <td>This tree points to group nodes.</td>
+ </tr>
+ <tr>
+ <td align=center>1</td>
+ <td>This tree points to raw data chunk nodes.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Node Level</td>
+ <td>
+ <P>The node level indicates the level at which this node
+ appears in the tree (leaf nodes are at level zero). Not
+ only does the level indicate whether child pointers
+ point to sub-trees or to data, but it can also be used
+ to help file consistency checking utilities reconstruct
+ damanged trees.
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Entries Used</td>
+ <td>
+ <P>This determines the number of children to which this
+ node points. All nodes of a particular type of tree
+ have the same maximum degree, but most nodes will point
+ to less than that number of children. The valid child
+ pointers and keys appear at the beginning of the node
+ and the unused pointers and keys appear at the end of
+ the node. The unused pointers and keys have undefined
+ values.
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Address of Left Sibling</td>
+ <td>
+ <P>This is the relative file address of the left sibling of
+ the current node. If the current
+ node is the left-most node at this level then this field
+ is the <A href="#UndefinedAddress">undefined address</A>.
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Address of Right Sibling</td>
+ <td>
+ <P>This is the relative file address of the right sibling of
+ the current node. If the current
+ node is the right-most node at this level then this
+ field is the <A href="#UndefinedAddress">undefined address</A>.
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Keys and Child Pointers</td>
+ <td>
+ <P>Each tree has 2<em>K</em>+1 keys with 2<em>K</em>
+ child pointers interleaved between the keys. The number
+ of keys and child pointers actually containing valid
+ values is determined by the node's <em>Entries Used</em> field.
+ If that field is <em>N</em> then the B-link tree contains
+ <em>N</em> child pointers and <em>N</em>+1 keys.
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Key</td>
+ <td>
+ <P>The format and size of the key values is determined by
+ the type of data to which this tree points. The keys are
+ ordered and are boundaries for the contents of the child
+ pointer; that is, the key values represented by child
+ <em>N</em> fall between Key <em>N</em> and Key
+ <em>N</em>+1. Whether the interval is open or closed on
+ each end is determined by the type of data to which the
+ tree points.
+ </P>
+
+ <P>
+ The format of the key depends on the node type.
+ For nodes of node type 0 (group nodes), the key is formatted as
+ follows:
+ <center>
+ <table class=list>
+ <tr>
+ <td width=30%>A single field of <i>Size of Lengths</i>
+ bytes:</td>
+ <td>Indicates the byte offset into the local heap
+ for the first object name in the subtree which
+ that key describes.
+ </td>
+ </tr>
+ </table>
+ </center>
+ </P>
+
+ <P>
+ For nodes of node type 1 (chunked raw data nodes), the key is
+ formatted as follows:
+ <center>
+ <table class=list>
+ <tr>
+ <td width=30%>Bytes 1-4:</td>
+ <td>Size of chunk in bytes.</td>
+ </tr>
+ <tr>
+ <td>Bytes 4-8:</td>
+ <td>Filter mask, a 32-bit bitfield indicating which
+ filters have been skipped for this chunk. Each filter
+ has an index number in the pipeline (starting at 0, with
+ the first filter to apply) and if that filter is skipped,
+ the bit corresponding to it's index is set.</td>
+ </tr>
+ <tr>
+ <td><em>N</em> 64-bit fields:</td>
+ <td>A 64-bit index indicating the offset of the
+ chunk within the dataset where <i>N</i> is the number
+ of dimensions of the dataset. For example, if
+ a chunk in a 3-dimensional dataset begins at the
+ position <code>[5,5,5]</code>, there will be three
+ such 64-bit indices, each with the value of
+ <code>5</code>.</td>
+ </tr>
+ </table>
+ </center>
+ </P>
+ </td>
+ </tr>
+
+ <tr valign=top>
+ <td>Child Pointer</td>
+ <td>
+ <P>The tree node contains file addresses of subtrees or
+ data depending on the node level. Nodes at Level 0 point
+ to data addresses, either raw data chunk or group nodes.
+ Nodes at non-zero levels point to other nodes of the
+ same B-tree.
+ </P>
+ <P>For raw data chunk nodes, the child pointer is the address
+ of a single raw data chunk. For group nodes, the child pointer
+ points to a <A href="#SymbolTable">symbol table</A>, which contains
+ information for multiple symbol table entries.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <p>
+ Conceptually, each B-tree node looks like this:
+ <center>
+ <table>
+ <tr valign=top align=center>
+ <td>key[0]</td><td>&nbsp;</td>
+ <td>child[0]</td><td>&nbsp;</td>
+ <td>key[1]</td><td>&nbsp;</td>
+ <td>child[1]</td><td>&nbsp;</td>
+ <td>key[2]</td><td>&nbsp;</td>
+ <td>...</td><td>&nbsp;</td>
+ <td>...</td><td>&nbsp;</td>
+ <td>key[<i>N</i>-1]</td><td>&nbsp;</td>
+ <td>child[<i>N</i>-1]</td><td>&nbsp;</td>
+ <td>key[<i>N</i>]</td>
+ </tr>
+ </table>
+ </center>
+ <br>
+
+ where child[<i>i</i>] is a pointer to a sub-tree (at a level
+ above Level 0) or to data (at Level 0).
+ Each key[<i>i</i>] describes an <i>item</i> stored by the B-tree
+ (a chunk or an object of a group node). The range of values
+ represented by child[<i>i</i>] is indicated by key[<i>i</i>]
+ and key[<i>i</i>+1].
+
+
+ <p>The following question must next be answered:
+ "Is the value described by key[<i>i</i>] contained in
+ child[<i>i</i>-1] or in child[<i>i</i>]?"
+ The answer depends on the type of tree.
+ In trees for groups (node type 0) the object described by
+ key[<i>i</i>] is the greatest object contained in
+ child[<i>i</i>-1] while in chunk trees (node type 1) the
+ chunk described by key[<i>i</i>] is the least chunk in
+ child[<i>i</i>].
+
+ <p>That means that key[0] for group trees is sometimes unused;
+ it points to offset zero in the heap, which is always the
+ empty string and compares as "less-than" any valid object name.
+
+ <p>And key[<i>N</i>] for chunk trees is sometimes unused;
+ it contains a chunk offset which compares as "greater-than"
+ any other chunk offset and has a chunk byte size of zero
+ to indicate that it is not actually allocated.
+
+
+ <h3><a name="SymbolTable">Disk Format: Level 1B - Group and Symbol Nodes</a></h3>
+
+ <p>A group is an object internal to the file that allows
+ arbitrary nesting of objects within the file (including other groups).
+ A group maps a set of names in the group to a set of relative
+ file addresses where objects with those names are located in
+ the file. Certain metadata for an object to which the group points
+ can be cached in the group's symbol table in addition to the
+ object's header.
+
+ <p>An HDF5 object name space can be stored hierarchically by
+ partitioning the name into components and storing each
+ component in a group. The group entry for a
+ non-ultimate component points to the group containing
+ the next component. The group entry for the last
+ component points to the object being named.
+
+ <p>A group is a collection of group nodes pointed
+ to by a B-link tree. Each group node contains entries
+ for one or more symbols. If an attempt is made to add a
+ symbol to an already full group node containing
+ 2<em>K</em> entries, then the node is split and one node
+ contains <em>K</em> symbols and the other contains
+ <em>K</em>+1 symbols.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Group Node (A Leaf of a B-tree)
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+
+ <tr>
+ <td colspan=4>Signature</td>
+
+ <tr>
+ <td>Version Number</td>
+ <td>Reserved (0)</td>
+ <td colspan=2>Number of Symbols</td>
+
+ <tr>
+ <td colspan=4><br><br>Group Entries<br><br><br></td>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Signature</td>
+ <td>
+ <P>The ASCII character string "<code>SNOD</code>" is
+ used to indicate the
+ beginning of a group node. This gives file
+ consistency checking utilities a better chance of
+ reconstructing a damaged file.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version Number</td>
+ <td>
+ <P>The version number for the group node. This
+ document describes version 1. (There is no version '0'
+ of the group node)
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Number of Symbols</td>
+ <td>
+ <P>Although all group nodes have the same length,
+ most contain fewer than the maximum possible number of
+ symbol entries. This field indicates how many entries
+ contain valid data. The valid entries are packed at the
+ beginning of the group node while the remaining
+ entries contain undefined values.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Group Entries</td>
+ <td>
+ <P>Each symbol has an entry in the group node.
+ The format of the entry is described below.
+ There are 2<EM>K</EM> entries in each group node, where
+ <EM>K</EM> is the "Group Leaf Node K" value from the
+ <A href="#SuperBlock">super block</A>.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <h3><a name="SymbolTableEntry">
+ Disk Format: Level 1C - Group Entry </a></h3>
+
+ <p>Each group entry in a group node is designed
+ to allow for very fast browsing of stored objects.
+ Toward that design goal, the group entries
+ include space for caching certain constant metadata from the
+ object header.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Group Entry
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Name Offset<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Object Header Address<sup>O</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Cache Type</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br><br>Scratch-pad Space (16 bytes)<br><br><br></td>
+ </tr>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'O' the above table are
+ <br>
+ of the size specified in "Size of Offsets.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Name Offset</td>
+ <td>
+ <P>This is the byte offset into the group local
+ heap for the name of the object. The name is null
+ terminated.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Object Header Address</td>
+ <td>
+ <P>Every object has an object header which serves as a
+ permanent location for the object's metadata. In addition
+ to appearing in the object header, some metadata can be
+ cached in the scratch-pad space.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Cache Type</td>
+ <td>
+ <P>The cache type is determined from the object header.
+ It also determines the format for the scratch-pad space:
+ <br>
+ <table class=list>
+ <tr align=left>
+ <th>Type:</th>
+ <th>Description:</th>
+ </tr>
+ <tr>
+ <td width="10%" align=center>0</td>
+ <td>No data is cached by the group entry. This
+ is guaranteed to be the case when an object header
+ has a link count greater than one.
+ </td>
+ </tr>
+ <tr>
+ <td align=center>1</td>
+ <td>Object header metadata is cached in the group
+ entry. This implies that the group
+ entry refers to another group.
+ </td>
+ </tr>
+ <tr>
+ <td align=center>2</td>
+ <td>The entry is a symbolic link. The first four bytes
+ of the scratch-pad space are the offset into the local
+ heap for the link value. The object header address
+ will be undefined.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><em>N</em></td>
+ <td>Other cache values can be defined later and
+ libraries that do not understand the new values will
+ still work properly.
+ </td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td>
+ <P>These four bytes are present so that the scratch-pad
+ space is aligned on an eight-byte boundary. They are
+ always set to zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Scratch-pad Space</td>
+ <td>
+ <P>This space is used for different purposes, depending
+ on the value of the Cache Type field. Any metadata
+ about a dataset object represented in the scratch-pad
+ space is duplicated in the object header for that
+ dataset. This metadata can include the datatype
+ and the size of the dataspace for a dataset whose datatype
+ is atomic and whose dataspace is fixed and less than
+ four dimensions.
+ </P>
+ <P>
+ Furthermore, no data is cached in the group
+ entry scratch-pad space if the object header for
+ the group entry has a link count greater than
+ one.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <h4>Format of the Scratch-pad Space</h4>
+
+ <p>The group entry scratch-pad space is formatted
+ according to the value in the Cache Type field.
+
+ <p>If the Cache Type field contains the value zero
+ <code>(0)</code> then no information is
+ stored in the scratch-pad space.
+
+ <p>If the Cache Type field contains the value one
+ <code>(1)</code>, then the scratch-pad space
+ contains cached metadata for another object header
+ in the following format:
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Object Header Scratch-pad Format
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+
+ <tr>
+ <td colspan=4>Address of B-tree<sup>O</sup></td>
+
+ <tr>
+ <td colspan=4>Address of Name Heap<sup>O</sup></td>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'O' the above table are
+ <br>
+ of the size specified in "Size of Offsets.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Address of B-tree</td>
+ <td>
+ <P>This is the file address for the root of the
+ group's B-tree.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Address of Name Heap</td>
+ <td>
+ <P>This is the file address for the group's local
+ heap, in which are stored the group's symbol names.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+
+ <P>If the Cache Type field contains the value two
+ <code>(2)</code>, then the scratch-pad space
+ contains cached metadata for another symbolic link
+ in the following format:
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Symbolic Link Scratch-pad Format
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Offset to Link Value</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Offset to Link Value</td>
+ <td>
+ <P>The value of a symbolic link (that is, the name of the
+ thing to which it points) is stored in the local heap.
+ This field is the 4-byte offset into the local heap for
+ the start of the link value, which is null terminated.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <h3><a name="LocalHeap">Disk Format: Level 1D - Local Heaps</a></h3>
+
+ <P>A heap is a collection of small heap objects. Objects can be
+ inserted and removed from the heap at any time.
+ The address of a heap does not change once the heap is created.
+ References to objects are stored in the group table;
+ the names of those objects are stored in the local heap.
+ </P>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Local Heap
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Signature</td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Data Segment Size<sup>L</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Offset to Head of Free-list<sup>L</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Address of Data Segment<sup>O</sup></td>
+ </tr>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'L' the above table are
+ <br>
+ of the size specified in "Size of Lengths.")
+ </td></tr>
+ <tr><td>
+ (Items marked with an 'O' the above table are
+ <br>
+ of the size specified in "Size of Offsets.")
+ </td></tr>
+ </table>
+ </div>
+
+ <p>
+ <center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Signature</td>
+ <td>
+ <P>The ASCII character string "<code>HEAP</code>"
+ is used to indicate the
+ beginning of a heap. This gives file consistency
+ checking utilities a better chance of reconstructing a
+ damaged file.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>Each local heap has its own version number so that new
+ heaps can be added to old files. This document
+ describes version zero (0) of the local heap.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Data Segment Size</td>
+ <td>
+ <P>The total amount of disk memory allocated for the heap
+ data. This may be larger than the amount of space
+ required by the objects stored in the heap. The extra
+ unused space in the heap holds a linked list of free blocks.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Offset to Head of Free-list</td>
+ <td>
+ <P>This is the offset within the heap data segment of the
+ first free block (or the
+ <A href="#UndefinedAddress">undefined address</A> if there is no
+ free block). The free block contains "Size of Lengths" bytes that
+ are the offset of the next free block (or the
+ value '1' if this is the
+ last free block) followed by "Size of Lengths" bytes that store
+ the size of this free block. The size of the free block includes
+ the space used to store the offset of the next free block and
+ the of the current block, making the minimum size of a free block
+ 2 * "Size of Lengths".
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Address of Data Segment</td>
+ <td>
+ <P>The data segment originally starts immediately after
+ the heap header, but if the data segment must grow as a
+ result of adding more objects, then the data segment may
+ be relocated, in its entirety, to another part of the
+ file.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </center>
+
+ <p>Objects within the heap should be aligned on an 8-byte boundary.
+
+ <h3><a name="GlobalHeap">Disk Format: Level 1E - Global Heap</a></h3>
+
+ <P>Each HDF5 file has a global heap which stores various types of
+ information which is typically shared between datasets. The
+ global heap was designed to satisfy these goals:
+
+ <ol type="A">
+ <li>Repeated access to a heap object must be efficient without
+ resulting in repeated file I/O requests. Since global heap
+ objects will typically be shared among several datasets, it is
+ probable that the object will be accessed repeatedly.
+ <li>Collections of related global heap objects should result in
+ fewer and larger I/O requests. For instance, a dataset of
+ object references will have a global heap object for each
+ reference. Reading the entire set of object references
+ should result in a few large I/O requests instead of one small
+ I/O request for each reference.
+ <li>It should be possible to remove objects from the global heap
+ and the resulting file hole should be eligible to be reclaimed
+ for other uses.
+ </ol>
+ </P>
+
+ <P>The implementation of the heap makes use of the memory
+ management already available at the file level and combines that
+ with a new top-level object called a <em>collection</em> to
+ achieve Goal B. The global heap is the set of all collections.
+ Each global heap object belongs to exactly one collection and
+ each collection contains one or more global heap objects. For
+ the purposes of disk I/O and caching, a collection is treated as
+ an atomic object.
+ </P>
+
+ <P>The HDF5 library creates global heap collections as needed, so there may
+ be multiple collections throughout the file. The set of all of them is
+ abstractly called the "global heap", although they don't actually link
+ to each other, and there is no global place in the file where you can
+ discover all of the collections. The collections are found simply by
+ finding a reference to one through another object in the file (eg.
+ variable-length datatype elements, etc).
+ </P>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ A Global Heap Collection
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Signature</td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Collection Size<sup>L</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Global Heap Object 1<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Global Heap Object 2<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>...<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Global Heap Object <em>N</em><br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Global Heap Object 0 (free space)<br><br></td>
+ </tr>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'L' the above table are
+ <br>
+ of the size specified in "Size of Lengths.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Signature</td>
+ <td>
+ <P>The ASCII character string "<code>GCOL</code>"
+ is used to indicate the
+ beginning of a collection. This gives file consistency
+ checking utilities a better chance of reconstructing a
+ damaged file.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>Each collection has its own version number so that new
+ collections can be added to old files. This document
+ describes version one (1) of the collections (there is no
+ version zero (0)).
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Collection Size</td>
+ <td>
+ <P>This is the size in bytes of the entire collection
+ including this field. The default (and minimum)
+ collection size is 4096 bytes which is a typical file
+ system block size. This allows for 127 16-byte heap
+ objects plus their overhead (the collection header of 16 bytes
+ and the 16 bytes of information about each heap object).
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Global Heap Object 1 through <em>N</em></td>
+ <td>
+ <P>The objects are stored in any order with no
+ intervening unused space.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Global Heap Object 0</td>
+ <td>
+ <P>Global Heap Object 0 (zero), when present, represents the free
+ space in the collection. Free space always appears at the end of
+ the collection. If the free space is too small to store the header
+ for Object 0 (described below) then the header is implied and the
+ collection contains no free space.
+ </P>
+ </td>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Global Heap Object
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Heap Object ID</td>
+ <td colspan=2>Reference Count</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Object Size<sup>L</sup></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Object Data<br><br></td>
+ </tr>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'L' the above table are
+ <br>
+ of the size specified in "Size of Lengths.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Heap Object ID</td>
+ <td>
+ <P>Each object has a unique identification number within a
+ collection. The identification numbers are chosen so that
+ new objects have the smallest value possible with the
+ exception that the identifier <code>0</code> always refers to the
+ object which represents all free space within the
+ collection.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reference Count</td>
+ <td>
+ <P>All heap objects have a reference count field. An
+ object which is referenced from some other part of the
+ file will have a positive reference count. The reference
+ count for Object 0 is always zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td>
+ <P>Zero padding to align next field on an 8-byte boundary.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Object Size</td>
+ <td>
+ <P>This is the size of the object data stored for the object.
+ The actual storage space allocated for the object data is rounded
+ up to a multiple of eight.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Object Data</td>
+ <td>
+ <P>The object data is treated as a one-dimensional array
+ of bytes to be interpreted by the caller.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <h3><a name="FreeSpaceIndex">Disk Format: Level 1F - Free-space Index</a></h3>
+
+ <p>The free-space index is a collection of blocks of data,
+ dispersed throughout the file, which are currently not used by
+ any file objects.
+
+ <p>The super block contains a pointer to root of the free-space description;
+ that pointer is currently required to be the
+ <A href="#UndefinedAddress">undefined address</A>.
+
+ <p>The format of the free-space index is not defined at this time.
+
+<!--
+ <p>The Free-space Index is a collection of blocks of data,
+ dispersed throughout the file, which are currently not used by
+ any file objects. The blocks of data are indexed by a B-tree of
+ their length within the file.
+
+
+ <p>Each B-tree page is composed of the following entries and
+ B-tree management information, organized as follows:
+
+ <p>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Free-space Heap Page</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4>Signature</td>
+ <tr align=center>
+ <td colspan=4>B-tree Left-link Offset</td>
+ <tr align=center>
+ <td colspan=4><br>Length of Free-block #1<br> <br></td>
+ <tr align=center>
+ <td colspan=4><br>Offset of Free-block #1<br> <br></td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4><br>Length of Free-block #n<br> <br></td>
+ <tr align=center>
+ <td colspan=4><br>Offset of Free-block #n<br> <br></td>
+ <tr align=center>
+ <td colspan=4>"High" Offset</td>
+ <tr align=center>
+ <td colspan=4>Right-link Offset</td>
+ </table>
+ </center>
+
+ <p>
+ <dl>
+ <dt> The elements of the free-space heap page are described below:
+ <dd>
+ <dl>
+ <dt>Signature: (4 bytes)
+ <dd>The ASCII character string <code>FREE</code>
+ is used to indicate the
+ beginning of a free-space heap B-tree page. This gives
+ file consistency checking utilities a better chance of
+ reconstructing a damaged file.
+
+ <dt>B-tree Left-link Offset: (&lt;offset&gt; bytes)
+ <dd>This value is used to indicate the offset of all offsets
+ in the B-link-tree which are smaller than the value of the
+ offset in entry #1. This value is also used to indicate a
+ leaf node in the B-link-tree by being set to all ones.
+
+ <dt>Length of Free-block #n: (&lt;length&gt; bytes)
+ <dd>This value indicates the length of an unused block in
+ the file.
+
+ <dt>Offset of Free-block #n: (&lt;offset&gt; bytes)
+ <dd>This value indicates the offset in the file of an
+ unused block in the file.
+
+ <dt>"High" Offset: (4-bytes)
+ <dd>This offset is used as the upper bound on offsets
+ contained within a page when the page has been split.
+
+ <dt>Right-link Offset: (&lt;offset&gt; bytes)
+ <dd>This value is used to indicate the offset of the next
+ child to the right of the parent of this group
+ page. When there is no node to the right, this value is
+ all zeros.
+ </dl>
+ </dl>
+
+ <p>The algorithms for searching and inserting objects in the
+ B-tree pages are described fully in the Lehman and Yao paper,
+ which should be read to provide a full description of the
+ B-tree's usage.
+-->
+
+ <BR>
+ <HR>
+
+ <h2><a name="DataObject">Disk Format: Level 2 - Data Objects </a></h2>
+
+ <P>Data objects contain the real information in the file. These
+ objects compose the scientific data and other information which
+ are generally thought of as "data" by the end-user. All the
+ other information in the file is provided as a framework for
+ these data objects.
+ </P>
+
+ <P>A data object is composed of header information and data
+ information. The header information contains the information
+ needed to interpret the data information for the data object as
+ well as additional "metadata" or pointers to additional
+ "metadata" used to describe or annotate each data object.
+ </P>
+
+ <h3><a name="ObjectHeader">
+ Disk Format: Level 2A - Data Object Headers</a></h3>
+
+ <P>The header information of an object is designed to encompass
+ all the information about an object, except for the data itself.
+ This information includes
+ the dataspace, datatype, information about how the data
+ is stored on disk (in external files, compressed, broken up in
+ blocks, etc.), as well as other information used by the library
+ to speed up access to the data objects or maintain a file's
+ integrity. Information stored by user applications as attributes
+ is also stored in the object's header. The header of each object is
+ not necessarily located immediately prior to the object's data in the
+ file and in fact may be located in any position in the file. The order
+ of the messages in an object header is not significant.
+ </P>
+
+ <P>Header messages are aligned on 8-byte boundaries.
+ </P>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Object Headers
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Reserved (zero)</td>
+ <td colspan=2>Number of Header Messages</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Object Reference Count</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Object Header Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Header Message Type #1</td>
+ <td colspan=2>Size of Header Message Data #1</td>
+ </tr>
+
+ <tr>
+ <td>Header Message #1 Flags</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Header Message Data #1<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Header Message Type #n</td>
+ <td colspan=2>Size of Header Message Data #n</td>
+ </tr>
+
+ <tr>
+ <td>Header Message #n Flags</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Header Message Data #n<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>This value is used to determine the format of the
+ information in the object header. When the format of the
+ information in the object header is changed, the version number
+ is incremented and can be used to determine how the
+ information in the object header is formatted. This
+ document describes version one (1) (there was no version
+ zero (0)).
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Number of Header Messages</td>
+ <td>
+ <P>This value determines the number of messages listed in
+ object headers for this object. This value includes the messages
+ in continuation messages for this object.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Object Reference Count</td>
+ <td>
+ <P>This value specifies the number of "hard links" to this object
+ within the current file. References to the object from external
+ files, "soft links" in this file and object references in this
+ file are not tracked.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Object Header Size</td>
+ <td>
+ <P>This value specifies the number of bytes of header message data
+ following this length field that contain object header messages
+ for this object header. This value does not include the size of
+ object header continuation blocks for this object elsewhere in the
+ file.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Header Message Type</td>
+ <td>
+ <P>This value specifies the type of information included in the
+ following header message data. The header message types for the
+ pre-defined header messages are included in sections below.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size of Header Message Data</td>
+ <td>
+ <P>This value specifies the number of bytes of header
+ message data following the header message type and length
+ information for the current message. The size includes
+ padding bytes to make the message a multiple of eight
+ bytes.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Header Message Flags</td>
+ <td>
+ <P>This is a bit field with the following definition:
+ <table class=list>
+ <tr>
+ <th width="30%">Bit</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>If set, the message data is constant. This is used
+ for messages like the datatype message of a dataset.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>If set, the message is stored in the global heap.
+ The Header Message Data field contains a Shared Object
+ message and the Size of Header Message Data field
+ contains the size of that Shared Object message.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>2-7</code></td>
+ <td>Reserved</td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Header Message Data</td>
+ <td>
+ <P>The format and length of this field is determined by the
+ header message type and size respectively. Some header
+ message types do not require any data and this information
+ can be eliminated by setting the length of the message to
+ zero. The data is padded with enough zeros to make the
+ size a multiple of eight.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <P>The header message types and the message data associated with
+ them compose the critical "metadata" about each object. Some
+ header messages are required for each object while others are
+ optional. Some optional header messages may also be repeated
+ several times in the header itself, the requirements and number
+ of times allowed in the header will be noted in each header
+ message description below.
+ </P>
+
+ <P>The following is a list of currently defined header messages:
+ </P>
+
+ <hr>
+ <h4><a name="NILMessage">Name: NIL</a></h4>
+
+ <P class=item><B>Header Message Type: </B>0x0000
+ </P>
+ <P class=item><B>Length:</B> varies
+ </P>
+ <P class=item><B>Status:</B> Optional, may be repeated.
+ </P>
+ <P class=item><B>Purpose and Description:</B> The NIL message is used to indicate a
+ message which is to be ignored when reading the header messages for a
+ data object. [Possibly one which has been deleted for some reason.]
+ </P>
+ <P class=item><B>Format of Data:</B> Unspecified.
+ </P>
+
+ <hr>
+ <h4><a name="SimpleDataSpace">Name: Simple Dataspace</a></h4>
+
+ <P class=item><B>Header Message Type: </B>0x0001
+ </P>
+ <P class=item><B>Length:</B> Varies according to the number of dimensions,
+ as described in the following table.
+ </P>
+ <P class=item><B>Status:</B> Required for dataset objects, may not be
+ repeated.
+ </P>
+ <P class=item><B>Description:</B> The simple dataspace message describes the
+ number of dimensions (i.e. "rank") and size of each dimension that the
+ data object has. This message is only used for datasets which have a
+ simple, rectilinear grid layout; datasets requiring a more complex
+ layout (irregularly structured or unstructured grids, etc.) must use
+ the <em>Complex Dataspace</em> message for expressing the space the
+ dataset inhabits. <i>(Note: The <em>Complex Dataspace</em>
+ functionality is not yet implemented and it is not described in this
+ document.)</i>
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Simple Dataspace Message
+ </caption>
+
+ <tr>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ <th>byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Dimensionality</td>
+ <td>Flags</td>
+ <td>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #1 Size<sup>L</sup></td>
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr>
+ <td colspan=4>Dimension #n Size<sup>L</sup></td>
+ <tr>
+ <td colspan=4>Dimension #1 Maximum Size<sup>L</sup></td>
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr>
+ <td colspan=4>Dimension #n Maximum Size<sup>L</sup></td>
+ <tr>
+ <td colspan=4>Permutation Index #1<sup>L</sup></td>
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr>
+ <td colspan=4>Permutation Index #n<sup>L</sup></td>
+ </table>
+
+ <table class=note>
+ <tr><td>
+ (Items marked with an 'L' the above table are
+ <br>
+ of the size specified in "Size of Lengths.")
+ </td></tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>This value is used to determine the format of the
+ Simple Dataspace Message. When the format of the
+ information in the message is changed, the version number
+ is incremented and can be used to determine how the
+ information in the object header is formatted. This
+ document describes version one (1) (there was no version
+ zero (0)).
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td>
+ <P>This value is the number of dimensions that the data
+ object has.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Flags</td>
+ <td>
+ <P>This field is used to store flags to indicate the
+ presence of parts of this message. Bit 0 (the least
+ significant bit) is used to indicate that maximum
+ dimensions are present. Bit 1 is used to indicate that
+ permutation indices are present.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimension #n Size</td>
+ <td>
+ <P>This value is the current size of the dimension of the
+ data as stored in the file. The first dimension stored in
+ the list of dimensions is the slowest changing dimension
+ and the last dimension stored is the fastest changing
+ dimension.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimension #n Maximum Size</td>
+ <td>
+ <P>This value is the maximum size of the dimension of the
+ data as stored in the file. This value may be the special
+ "<A href="#UnlimitedDim">unlimited</A>" size which indicates
+ that the data may expand along this dimension indefinitely.
+ If these values are not stored, the maximum size of each
+ dimension is assumed to be the dimension's current size.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Permutation Index #n</td>
+ <td>
+ <P>This value is the index permutation used to map
+ each dimension from the canonical representation to an
+ alternate axis for each dimension. If these values are
+ not stored, the first dimension stored in the list of
+ dimensions is the slowest changing dimension and the last
+ dimension stored is the fastest changing dimension.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ </P>
+
+<!--
+ <hr>
+ <h4><a name="DataSpaceMessage">Name: Complex Dataspace (Fiber Bundle?)</a></h4>
+ <b>Header Message Type: </b>0x0002<br>
+ <b>Length:</b> varies<br>
+
+ <b>Status:</b> One of the <em>Simple Dataspace</em> or
+ <em>Complex Dataspace</em> messages is required (but not both) and may
+ not be repeated.<br> <b>Purpose and Description:</b> The
+ <em>Dataspace</em> message describes space that the dataset is
+ mapped onto in a more comprehensive way than the <em>Simple
+ Dimensionality</em> message is capable of handling. The
+ dataspace of a dataset encompasses the type of coordinate system
+ used to locate the dataset's elements as well as the structure and
+ regularity of the coordinate system. The dataspace also
+ describes the number of dimensions which the dataset inhabits as
+ well as a possible higher dimensional space in which the dataset
+ is located within.
+
+ <br>
+ <b>Format of Data:</b>
+
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Dataspace Message Layout</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4>Mesh Type</td>
+ <tr align=center>
+ <td colspan=4>Logical Dimensionality</td>
+ </table>
+ </center>
+
+ <p>
+ <dl>
+ <dt>The elements of the dimensionality message are described below:
+ <dd>
+ <dl>
+ <dt>Mesh Type: (unsigned 32-bit integer)
+ <dd>This value indicates whether the grid is
+ polar/spherical/cartesion,
+ structured/unstructured and regular/irregular. <br>
+ The mesh type value is broken up as follows: <br>
+
+ <P>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Mesh-type Layout</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=1>Mesh Embedding</td>
+ <td colspan=1>Coordinate System</td>
+ <td colspan=1>Structure</td>
+ <td colspan=1>Regularity</td>
+ </table>
+ </center>
+ The following are the definitions of mesh-type bytes:
+ <dl>
+ <dt>Mesh Embedding
+ <dd>This value indicates whether the dataset dataspace
+ is located within
+ another dataspace or not:
+ <dl> <dl>
+ <dt>&lt;STANDALONE&gt;
+ <dd>The dataset mesh is self-contained and is not
+ embedded in another mesh.
+ <dt>&lt;EMBEDDED&gt;
+ <dd>The dataset's dataspace is located within
+ another dataspace, as
+ described in information below.
+ </dl> </dl>
+ <dt>Coordinate System
+ <dd>This value defines the type of coordinate system
+ used for the mesh:
+ <dl> <dl>
+ <dt>&lt;POLAR&gt;
+ <dd>The last two dimensions are in polar
+ coordinates, higher dimensions are
+ cartesian.
+ <dt>&lt;SPHERICAL&gt;
+ <dd>The last three dimensions are in spherical
+ coordinates, higher dimensions
+ are cartesian.
+ <dt>&lt;CARTESIAN&gt;
+ <dd>All dimensions are in cartesian coordinates.
+ </dl> </dl>
+ <dt>Structure
+ <dd>This value defines the locations of the grid-points
+ on the axes:
+ <dl> <dl>
+ <dt>&lt;STRUCTURED&gt;
+ <dd>All grid-points are on integral, sequential
+ locations, starting from 0.
+ <dt>&lt;UNSTRUCTURED&gt;
+ <dd>Grid-points locations in each dimension are
+ explicitly defined and
+ may be of any numeric datatype.
+ </dl> </dl>
+ <dt>Regularity
+ <dd>This value defines the locations of the dataset
+ points on the grid:
+ <dl> <dl>
+ <dt>&lt;REGULAR&gt;
+ <dd>All dataset elements are located at the
+ grid-points defined.
+ <dt>&lt;IRREGULAR&gt;
+ <dd>Each dataset element has a particular
+ grid-location defined.
+ </dl> </dl>
+ </dl>
+ <p>The following grid combinations are currently allowed:
+ <dl> <dl>
+ <dt>&lt;POLAR-STRUCTURED-REGULAR&gt;
+ <dt>&lt;SPHERICAL-STRUCTURED-REGULAR&gt;
+ <dt>&lt;CARTESIAN-STRUCTURED-REGULAR&gt;
+ <dt>&lt;POLAR-UNSTRUCTURED-REGULAR&gt;
+ <dt>&lt;SPHERICAL-UNSTRUCTURED-REGULAR&gt;
+ <dt>&lt;CARTESIAN-UNSTRUCTURED-REGULAR&gt;
+ <dt>&lt;CARTESIAN-UNSTRUCTURED-IRREGULAR&gt;
+ </dl> </dl>
+ All of the above grid types can be embedded within another
+ dataspace.
+ <br> <br>
+ <dt>Logical Dimensionality: (unsigned 32-bit integer)
+ <dd>This value is the number of dimensions that the dataset occupies.
+
+ <P>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Dataspace Embedded Dimensionality Information</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4>Embedded Dimensionality</td>
+ <tr align=center>
+ <td colspan=4>Embedded Dimension Size #1</td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4>Embedded Dimension Size #n</td>
+ <tr align=center>
+ <td colspan=4>Embedded Origin Location #1</td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4>Embedded Origin Location #n</td>
+ </table>
+ </center>
+
+ <dt>Embedded Dimensionality: (unsigned 32-bit integer)
+ <dd>This value is the number of dimensions of the space the
+ dataset is located
+ within. i.e. a planar dataset located within a 3-D space,
+ or a 3-D dataset
+ which is a subset of another 3-D space, etc.
+ <dt>Embedded Dimension Size: (unsigned 32-bit integer)
+ <dd>These values are the sizes of the dimensions of the
+ embedded dataspace
+ that the dataset is located within.
+ <dt>Embedded Origin Location: (unsigned 32-bit integer)
+ <dd>These values comprise the location of the dataset's
+ origin within the embedded dataspace.
+ </dl>
+ </dl>
+ [Comment: need some way to handle different orientations of the
+ dataset dataspace
+ within the embedded dataspace]<br>
+
+ <P>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Dataspace Structured/Regular Grid Information</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4>Logical Dimension Size #1</td>
+ <tr align=center>
+ <td colspan=4>Logical Dimension Maximum #1</td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4>Logical Dimension Size #n</td>
+ <tr align=center>
+ <td colspan=4>Logical Dimension Maximum #n</td>
+ </table>
+ </center>
+
+ <p>
+ <dl>
+ <dt>The elements of the dimensionality message are described below:
+ <dd>
+ <dl>
+ <dt>Logical Dimension Size #n: (unsigned 32-bit integer)
+ <dd>This value is the current size of the dimension of the
+ data as stored in
+ the file. The first dimension stored in the list of
+ dimensions is the slowest
+ changing dimension and the last dimension stored is the
+ fastest changing
+ dimension.
+ <dt>Logical Dimension Maximum #n: (unsigned 32-bit integer)
+ <dd>This value is the maximum size of the dimension of the
+ data as stored in
+ the file. This value may be the special value
+ &lt;UNLIMITED&gt; which
+ indicates that the data may expand along this dimension
+ indefinitely.
+ </dl>
+ </dl>
+ <P>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Dataspace Structured/Irregular Grid Information</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4># of Grid Points in Dimension #1</td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4># of Grid Points in Dimension #n</td>
+ <tr align=center>
+ <td colspan=4>Datatype of Grid Point Locations</td>
+ <tr align=center>
+ <td colspan=4>Location of Grid Points in Dimension #1</td>
+ <tr align=center>
+ <td colspan=4>.<br>.<br>.<br></td>
+ <tr align=center>
+ <td colspan=4>Location of Grid Points in Dimension #n</td>
+ </table>
+ </center>
+
+ <P>
+ <center>
+ <table border cellpadding=4 width="80%">
+ <caption align=bottom>
+ <B>HDF5 Dataspace Unstructured Grid Information</B>
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+
+ <tr align=center>
+ <td colspan=4># of Grid Points</td>
+ <tr align=center>
+ <td colspan=4>Datatype of Grid Point Locations</td>
+ <tr align=center>
+ <td colspan=4>Grid Point Locations<br>.<br>.<br></td>
+ </table>
+ </center>
+-->
+
+ <hr>
+ <h4><a name="ReservedMessage_0002">Name: Reserved - Not Assigned Yet</a></h4>
+ <b>Header Message Type:</b> 0x0002<BR>
+ <b>Length:</b> N/A<BR>
+ <b>Status:</b> N/A<BR>
+ <b>Format of Data:</b> N/A<BR>
+
+ <p><b>Purpose and Description:</b> This message type was skipped during
+ the initial specification of the file format and may be used in a
+ future expansion to the format.
+
+
+ <hr>
+ <h4><a name="DataTypeMessage">Name: Datatype</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x0003
+ </P>
+ <P class=item><B>Length:</B> variable
+ </P>
+ <P class=item><B>Status:</B> Required for dataset or named datatype objects,
+ may not be repeated.
+ </P>
+
+ <P class=item><B>Description:</B> The datatype message defines the datatype
+ for each element of a dataset. A datatype can describe an atomic type
+ like a fixed- or floating-point type or a compound type like a C
+ struct.
+ Datatypes messages are stored
+ as a list of datatype classes and
+ their associated properties.
+ </P>
+
+ <P class=item2>Datatype messages that are part of a dataset object,
+ do not describe how elements are related to one another, the dataspace
+ message is used for that purpose. Datatype messages that are part of
+ a named datatype message describe an "abstract" datatype that can be
+ used by other objects in the file.
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Datatype Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Class and Version</td>
+ <td>Class Bit Field, Bits 0-7</td>
+ <td>Class Bit Field, Bits 8-15</td>
+ <td>Class Bit Field, Bits 16-23</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br><br>Properties<br><br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Class and Version</td>
+ <td>
+ <P>The version of the datatype message and the datatype's class
+ information are packed together in this field. The version
+ number is packed in the top 4 bits of the field and the class
+ is contained in the bottom 4 bits.
+ </P>
+ <P>The version number information is used for changes in the
+ format of the datatype message and is described here:
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by early versions of the library to encode
+ compound datatypes with explicit array fields.
+ See the compound datatype description below for
+ further details.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>The current version used by the library.
+ </td>
+ </tr>
+ </table>
+ </P>
+ <P>The class of the datatype determines the format for the class
+ bit field and properties portion of the datatype message, which
+ are described below. The
+ following classes are currently defined:
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Fixed-Point</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Floating-Point</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Time</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>3</code></td>
+ <td>String</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>4</code></td>
+ <td>Bitfield</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>5</code></td>
+ <td>Opaque</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>6</code></td>
+ <td>Compound</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>7</code></td>
+ <td>Reference</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>8</code></td>
+ <td>Enumerated</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>9</code></td>
+ <td>Variable-Length</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>10</code></td>
+ <td>Array</td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Class Bit Fields</td>
+ <td>
+ <P>The information in these bit fields is specific to each datatype
+ class and is described below. All bits not defined for a
+ datatype class are set to zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td>
+ <P>The size of the datatype in bytes.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Properties</td>
+ <td>
+ <P>This variable-sized field encodes information specific to each
+ datatype class and is described below. If there is no
+ property information specified for a datatype class, the size
+ of this field is zero.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Fixed-Point Numbers (Class 0):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0</td>
+ <td><b>Byte Order.</b> If zero, byte order is little-endian;
+ otherwise, byte order is big endian.</td>
+ </tr>
+
+ <tr>
+ <td>1, 2</td>
+ <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2
+ is the hi_pad type. If a datum has unused bits at either
+ end, then the lo_pad or hi_pad bit is copied to those
+ locations.</td>
+ </tr>
+
+ <tr>
+ <td>3</td>
+ <td><b>Signed.</b> If this bit is set then the fixed-point
+ number is in 2's complement form.</td>
+ </tr>
+
+ <tr>
+ <td>4-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Bit Offset</td>
+ <td colspan=2>Bit Precision</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Bit Offset</td>
+ <td>
+ <P>The bit offset of the first significant bit of the fixed-point
+ value within the datatype. The bit offset specifies the number
+ of bits "to the right of" the value.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Bit Precision</td>
+ <td>
+ <P>The number of bits of precision of the fixed-point value
+ within the datatype.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Floating-Point Numbers (Class 1):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0</td>
+ <td><b>Byte Order.</b> If zero, byte order is little-endian;
+ otherwise, byte order is big endian.</td>
+ </tr>
+
+ <tr>
+ <td>1, 2, 3</td>
+ <td><b>Padding type.</b> Bit 1 is the low bits pad type, bit 2
+ is the high bits pad type, and bit 3 is the internal bits
+ pad type. If a datum has unused bits at either end or between
+ the sign bit, exponent, or mantissa, then the value of bit
+ 1, 2, or 3 is copied to those locations.</td>
+ </tr>
+
+ <tr>
+ <td>4-5</td>
+ <td><b>Normalization.</b> The value can be 0 if there is no
+ normalization, 1 if the most significant bit of the
+ mantissa is always set (except for 0.0), and 2 if the most
+ signficant bit of the mantissa is not stored but is
+ implied to be set. The value 3 is reserved and will not
+ appear in this field.</td>
+ </tr>
+
+ <tr>
+ <td>6-7</td>
+ <td>Reserved (zero).</td>
+ </tr>
+
+ <tr>
+ <td>8-15</td>
+ <td><b>Sign Location.</b> This is the bit position of the sign
+ bit. Bits are numbered with the least significant bit zero.</td>
+ </tr>
+
+ <tr>
+ <td>16-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Bit Offset</td>
+ <td colspan=2>Bit Precision</td>
+ </tr>
+
+ <tr>
+ <td>Exponent Location</td>
+ <td>Exponent Size</td>
+ <td>Mantissa Location</td>
+ <td>Mantissa Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Exponent Bias</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Bit Offset</td>
+ <td>
+ <P>The bit offset of the first significant bit of the floating-point
+ value within the datatype. The bit offset specifies the number
+ of bits "to the right of" the value.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Bit Precision</td>
+ <td>
+ <P>The number of bits of precision of the floating-point value
+ within the datatype.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Exponent Location</td>
+ <td>
+ <P>The bit position of the exponent field. Bits are numbered with
+ the least significant bit number zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Exponent Size</td>
+ <td>
+ <P>The size of the exponent field in bits.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Mantissa Location</td>
+ <td>
+ <P>The bit position of the mantissa field. Bits are numbered with
+ the least significant bit number zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Mantissa Size</td>
+ <td>
+ <P>The size of the mantissa field in bits.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Exponent Bias</td>
+ <td>
+ <P>The bias of the exponent field.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Time (Class 2):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0</td>
+ <td><b>Byte Order.</b> If zero, byte order is little-endian;
+ otherwise, byte order is big endian.</td>
+ </tr>
+
+ <tr>
+ <td>1-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Bit Precision</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Bit Precision</td>
+ <td>
+ <P>The number of bits of precision of the time value.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Strings (Class 3):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-3</td>
+ <td><b>Padding type.</b> This four-bit value determines the
+ type of padding to use for the string. The values are:
+
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Null Terminate: A zero byte marks the end of the
+ string and is guaranteed to be present after
+ converting a long string to a short string. When
+ converting a short string to a long string the value is
+ padded with additional null characters as necessary.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Null Pad: Null characters are added to the end of
+ the value during conversions from short values to long
+ values but conversion in the opposite direction simply
+ truncates the value.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Space Pad: Space characters are added to the end of
+ the value during conversions from short values to long
+ values but conversion in the opposite direction simply
+ truncates the value. This is the Fortran
+ representation of the string.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>3-15</code></td>
+ <td>Reserved
+ </td>
+ </tr>
+ </table>
+ </tr>
+
+ <tr>
+ <td>4-7</td>
+ <td><b>Character Set.</b> The character set to use for
+ encoding the string. The only character set supported is
+ the 8-bit ASCII (zero) so no translations have been defined
+ yet.</td>
+ </tr>
+
+ <tr>
+ <td>8-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <P>There are no properties defined for the string class.
+ </P>
+ </P>
+
+ <P>Class specific information for Bitfields (Class 4):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0</td>
+ <td><b>Byte Order.</b> If zero, byte order is little-endian;
+ otherwise, byte order is big endian.</td>
+ </tr>
+
+ <tr>
+ <td>1, 2</td>
+ <td><b>Padding type.</b> Bit 1 is the lo_pad type and bit 2
+ is the hi_pad type. If a datum has unused bits at either
+ end, then the lo_pad or hi_pad bit is copied to those
+ locations.</td>
+ </tr>
+
+ <tr>
+ <td>3-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Description
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Bit Offset</td>
+ <td colspan=2>Bit Precision</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Bit Offset</td>
+ <td>
+ <P>The bit offset of the first significant bit of the bitfield
+ within the datatype. The bit offset specifies the number
+ of bits "to the right of" the value.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Bit Precision</td>
+ <td>
+ <P>The number of bits of precision of the bitfield
+ within the datatype.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Opaque (Class 5):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-7</td>
+ <td>Length of ASCII tag in bytes.</td>
+ </tr>
+
+ <tr>
+ <td>8-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Description
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>ASCII Tag<br>
+ <br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>ASCII Tag</td>
+ <td>
+ <P>This NUL-terminated string provides a description for the
+ opaque type. It is NUL-padded to a multiple of 8 bytes.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Compound (Class 6):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-15</td>
+ <td><b>Number of Members.</b> This field contains the number
+ of members defined for the compound datatype. The member
+ definitions are listed in the Properties field of the data
+ type message.
+ </tr>
+
+ <tr>
+ <td>15-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+ </P>
+
+ <P>The Properties field of a compound datatype is a list of the
+ member definitions of the compound datatype. The member
+ definitions appear one after another with no intervening bytes.
+ The member types are described with a recursive datatype
+ message.
+
+ <P>Note that the property descriptions are different for different
+ versions of the datatype version. Additionally note that the version
+ 0 properties are deprecated and have been replaced with the version
+ 1 properties in versions of the HDF5 library from the 1.4 release
+ onward.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Properties Description for Datatype Version 1
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Byte Offset of Member</td>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension Permutation</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #1 Size (required)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #2 Size (required)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #3 Size (required)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #4 Size (required)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Member Type Message<br><br></td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td>
+ <P>This NUL-terminated string provides a description for the
+ opaque type. It is NUL-padded to a multiple of 8 bytes.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Byte Offset of Member</td>
+ <td>
+ <P>This is the byte offset of the member within the datatype.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td>
+ <P>If set to zero, this field indicates a scalar member. If set
+ to a value greater than zero, this field indicates that the
+ member is an array of values. For array members, the size of
+ the array is indicated by the 'Size of Dimension n' field in
+ this message.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimension Permutation</td>
+ <td>
+ <P>This field was intended to allow an array field to have
+ it's dimensions permuted, but this was never implemented.
+ This field should always be set to zero.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimension #n Size</td>
+ <td>
+ <P>This field is the size of a dimension of the array field as
+ stored in the file. The first dimension stored in the list of
+ dimensions is the slowest changing dimension and the last
+ dimension stored is the fastest changing dimension.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Member Type Message</td>
+ <td>
+ <P>This field is a datatype message describing the datatype of
+ the member.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Properties Description for Datatype Version 2
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Byte Offset of Member</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Member Type Message<br><br></td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td>
+ <P>This NUL-terminated string provides a description for the
+ opaque type. It is NUL-padded to a multiple of 8 bytes.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Byte Offset of Member</td>
+ <td>
+ <P>This is the byte offset of the member within the datatype.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Member Type Message</td>
+ <td>
+ <P>This field is a datatype message describing the datatype of
+ the member.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Reference (Class 7):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-3</td>
+ <td><b>Type.</b> This four-bit value contains the type of reference
+ described. The values defined are:
+
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Object Reference: A reference to another object in this
+ HDF5 file.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Dataset Region Reference: A reference to a region within
+ a dataset in this HDF5 file.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Internal Reference: A reference to a region within the
+ current dataset. (Not currently implemented)
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>3-15</code></td>
+ <td>Reserved
+ </td>
+ </tr>
+ </table>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td>15-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <P>There are no properties defined for the reference class.
+ </P>
+ </P>
+
+ <P>Class specific information for Enumeration (Class 8):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-15</td>
+ <td><b>Number of Members.</b> The number of name/value
+ pairs defined for the enumeration type.</td>
+ </tr>
+
+ <tr>
+ <td>16-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Description
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Base Type<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Names<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Values<br><br></td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Base Type</td>
+ <td>
+ <P>Each enumeration type is based on some parent type, usually an
+ integer. The information for that parent type is described
+ recursively by this field.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Names</td>
+ <td>
+ <P>The name for each name/value pair. Each name is stored as a null
+ terminated ASCII string in a multiple of eight bytes. The names
+ are in no particular order.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Values</td>
+ <td>
+ <P>The list of values in the same order as the names. The values
+ are packed (no inter-value padding) and the size of each value
+ is determined by the parent type.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+
+ <P>Class specific information for Variable-Length (Class 9):
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <caption>
+ Bit Field Description
+ </caption>
+
+ <tr>
+ <th width="10%">Bits</th>
+ <th>Meaning</th>
+ </tr>
+
+ <tr>
+ <td>0-3</td>
+ <td><b>Type.</b> This four-bit value contains the type of
+ variable-length datatype described. The values defined are:
+
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Sequence: A variable-length sequence of any sequence of
+ data. Variable-length sequences do not have padding or
+ character set information.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>String: A variable-length sequence of characters.
+ Variable-length strings have padding and character set
+ information.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2-15</code></td>
+ <td>Reserved
+ </td>
+ </tr>
+ </table>
+
+ </td>
+ </tr>
+
+ <tr>
+ <td>4-7</td>
+ <td><b>Padding type.</b> (variable-length string only)
+ This four-bit value determines the type of padding
+ used for variable-length strings. The values are the same
+ as for the string padding type, as follows:
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Null terminate: A zero byte marks the end of a string
+ and is guaranteed to be present after converting a long
+ string to a short string. When converting a short string
+ to a long string, the value is padded with additional null
+ characters as necessary.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Null pad: Null characters are added to the end of the
+ value during conversion from a short string to a longer
+ string. Conversion from a long string to a shorter string
+ simply truncates the value.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Space pad: Space characters are added to the end of the
+ value during conversion from a short string to a longer
+ string. Conversion from a long string to a shorter string
+ simply truncates the value. This is the Fortran
+ representation of the string.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>3-15</code></td>
+ <td>Reserved
+ </td>
+ </tr>
+ </table>
+
+ This value is set to zero for variable-length sequences.
+
+ </td>
+ </tr>
+
+ <tr>
+ <td>8-11</td>
+ <td><b>Character Set.</b> (variable-length string only)
+ This four-bit value specifies the character set
+ to be used for encoding the string:
+ <table width=100% class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>ASCII: As of this writing (July 2003, Release 1.6.0),
+ 8-bit ASCII is the only character set supported. Therefore,
+ no translations have been defined.
+ </td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1-15</code></td>
+ <td>Reserved
+ </td>
+ </tr>
+ </table>
+
+ This value is set to zero for variable-length sequences.
+
+ </td>
+ </tr>
+
+ <tr>
+ <td>12-23</td>
+ <td>Reserved (zero).</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Description
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Base Type<br><br></td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Base Type</td>
+ <td>
+ <P>Each variable-length type is based on some parent type. The
+ information for that parent type is described recursively by
+ this field.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+ </P>
+
+ <P>Class specific information for Array (Class 10):
+
+ <P>There are no bit fields defined for the array class.
+ </P>
+
+ <P>Note that the dimension information defined in the property for this
+ datatype class is independent of dataspace information for a dataset.
+ The dimension information here describes the dimensionality of the
+ information within a data element (or a component of an element, if the
+ array datatype is nested within another datatype) and the dataspace for a
+ dataset describes the location of the elements in a dataset.
+ </P>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Description
+ </caption>
+
+ <tr>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ <th width="25%">Byte</th>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td colspan=3>Reserved (zero)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension #1 Size</td>
+ </tr>
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ </tr>
+ <tr>
+ <td colspan=4>Dimension #n Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Permutation Index #1</td>
+ </tr>
+ <tr>
+ <td colspan=4>.<br>.<br>.<br></td>
+ </tr>
+ <tr>
+ <td colspan=4>Permutation Index #n</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Base Type<br><br></td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td>
+ <P>This value is the number of dimensions that the array has.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimension #n Size</td>
+ <td>
+ <P>This value is the size of the dimension of the array
+ as stored in the file. The first dimension stored in
+ the list of dimensions is the slowest changing dimension
+ and the last dimension stored is the fastest changing
+ dimension.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Permutation Index #n</td>
+ <td>
+ <P>This value is the index permutation used to map
+ each dimension from the canonical representation to an
+ alternate axis for each dimension. Currently, dimension
+ permutations are not supported and these indices should be set
+ to the index position minus one (i.e. the first dimension should
+ be set to 0, the second dimension should be set to 1, etc.)
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Base Type</td>
+ <td>
+ <P>Each array type is based on some parent type. The
+ information for that parent type is described recursively by
+ this field.
+ </P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+
+ </P>
+
+ <hr>
+ <h4><a name="OldFillValueMessage">Name: Data Storage - Fill Value (Old)</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x0004
+ </P>
+ <P class=item><B>Length:</B> varies
+ </P>
+ <P class=item><B>Status:</B> Optional, may not be repeated.
+ </P>
+
+ <P class=item><B>Description:</B> The fill value message stores a single
+ data value which is returned to the application when an uninitialized
+ data element is read from a dataset. The fill value is interpreted
+ with the same datatype as the dataset. If no fill value message is
+ present then a fill value of all zero bytes is assumed.
+ </P>
+
+ <P class=item2>This fill value message is deprecated in favor of the "new"
+ fill value message (Message Type 0x0005) and is only written to the
+ file for forward compatibility with versions of the HDF5 library before
+ the 1.6.0 version. Additionally, it only appears for datasets with a
+ user defined fill value (as opposed to the library default fill value
+ or an explicitly set "undefined" fill value).
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Fill Value Message (Old)
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Fill Value<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td>
+ <P>This is the size of the Fill Value field in bytes.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Fill Value</td>
+ <td>
+ <P>The fill value. The bytes of the fill value are interpreted
+ using the same datatype as for the dataset.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+ </P>
+
+ <hr>
+ <h4><a name="FillValueMessage">Name: Data Storage - Fill Value </a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x0005
+ </P>
+ <P class=item><B>Length:</B> varies
+ </P>
+ <P class=item><B>Status:</B> Required for dataset objects, may not be repeated.
+ </P>
+
+ <P class=item><B>Description:</B> The fill value message stores a single
+ data value which is returned to the application when an uninitialized
+ data element is read from a dataset. The fill value is interpreted
+ with the same datatype as the dataset.
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Fill Value Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Space Allocation Time</td>
+ <td>Fill Value Write Time</td>
+ <td>Fill Value Defined</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Fill Value<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>The version number information is used for changes in the
+ format of the fill value message and is described here:
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by version 1.6.x of the library to encode
+ fill values. In this version, the Size field is
+ always present.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>The current version used by the library (version
+ 1.7.3 or later). In this version, the Size and
+ Fill Value fields are
+ only present if the Fill Value Defined field is set
+ to 1.
+ </td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Space Allocation Time</td>
+ <td>
+ <P>When the storage space for the dataset's raw data will be
+ allocated. The allowed values are:
+ <table class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Early allocation. Storage space for the entire dataset
+ should be allocated in the file when the dataset is
+ created.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Late allocation. Storage space for the entire dataset
+ should not be allocated until the dataset is written
+ to.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>3</code></td>
+ <td>Incremental allocation. Storage space for the
+ dataset should not be allocated until the portion
+ of the dataset is written to. This is currently
+ used in conjunction with chunked data storage for
+ datasets.
+ </td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Fill Value Write Time</td>
+ <td>
+ <P>At the time that storage space for the dataset's raw data is
+ allocated, this value indicates whether the fill value should
+ be written to the raw data storage elements. The allowed values
+ are:
+ <table class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>On allocation. The fill value is always written to
+ the raw data storage when the storage space is allocated.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Never. The fill value should never be written to
+ the raw data storage.
+ </td>
+ </tr>
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Fill value written if set by user. The fill value
+ will be written to the raw data storage when the storage
+ space is allocated only if the user explicitly set
+ the fill value. If the fill value is the library
+ default or is undefined, it will not be written to
+ the raw data storage.
+ </td>
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Fill Value Defined</td>
+ <td>
+ <P>This value indicates if a fill value is defined for this
+ dataset. If this value is 0, the fill value is undefined.
+ If this value is 1, a fill value is defined for this dataset.
+ For version 2 or later of the fill value message, this value
+ controls the presence of the Size field.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td>
+ <P>This is the size of the Fill Value field in bytes. This field
+ is not present if the Version field is >1 and the Fill Value
+ Defined field is set to 0.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Fill Value</td>
+ <td>
+ <P>The fill value. The bytes of the fill value are interpreted
+ using the same datatype as for the dataset. This field is
+ not present if the Version field is >1 and the Fill Value
+ Defined field is set to 0.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+ </P>
+
+<!--
+ <hr>
+ <h4><a name="CompactDataStorageMessage">Name: Data Storage - Compact</a></h4>
+
+ <b>Header Message Type:</b> 0x0006<br>
+ <b>Length:</b> varies<br>
+ <b>Status:</b> Optional, may not be repeated.<br>
+
+ <p>This message indicates that the data for the data object is
+ stored within the current HDF file by including the actual
+ data as the header data for this message. The data is
+ stored internally in
+ the <em>normal format</em>, i.e. in one chunk, uncompressed, etc.
+
+ <P>Note that one and only one of the <em>Data Storage</em> headers can be
+ stored for each data object.
+
+ <P><b>Format of Data:</b> The message data is actually composed
+ of dataset data, so the format will be determined by the dataset
+ format.
+-->
+
+ <hr>
+ <h4><a name="ReservedMessage_0006">Name: Reserved - Not Assigned Yet</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0006</P>
+ <P class=item><B>Length:</B> N/A</P>
+ <P class=item><B>Status:</B> N/A</P>
+ <P class=item><B>Format of Data:</B> N/A</P>
+
+ <P class=item><B>Purpose and Description:</B> This message type was skipped during
+ the initial specification of the file format and may be used in a
+ future expansion to the format.</P>
+
+ <hr>
+ <h4><a name="ExternalFileListMessage">Name: Data Storage -
+ External Data Files</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0007 </P>
+ <P class=item><B>Length:</B> varies</P>
+ <P class=item><B>Status:</B> Optional, may not be repeated.</P>
+
+ <P class=item><B>Purpose and Description:</B> The external object message
+ indicates that the data for an object is stored outside the HDF5
+ file. The filename of the object is stored as a Universal
+ Resource Location (URL) of the actual filename containing the
+ data. An external file list record also contains the byte offset
+ of the start of the data within the file and the amount of space
+ reserved in the file for that data.</P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ External File List Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td colspan=3>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Allocated Slots</td>
+ <td colspan=2>Used Slots</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Heap Address<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Slot Definitions...<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>The version number information is used for changes in the format of External File
+ List Message and is described here:
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used.
+ </tr>
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>The current version used by the library.
+ </tr>
+ </table>
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td>
+ <P>This field is reserved for future use.</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Allocated Slots</td>
+ <td>
+ <P>The total number of slots allocated in the message. Its value must be at least as
+ large as the value contained in the Used Slots field. (The current library simply
+ uses the number of Used Slots for this message)</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Used Slots</td>
+ <td>
+ <P>The number of initial slots which contains valid information.</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Heap Address</td>
+ <td>
+ <P>This is the address of a local heap which contains the names for the external
+ files (The local heap information can be found in Disk Format Level 1D in this
+ document). The name at offset zero in the heap is always the empty string.</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Slot Definitions</td>
+ <td>
+ <P>The slot definitions are stored in order according to the array addresses they
+ represent.</P>
+ </td>
+ </tr>
+
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ External File List Slot
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name Offset(&lt;size&gt; bytes)<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>File Offset(&lt;size&gt; bytes)<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Size<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Name Offset(&lt;size&gt; bytes)</td>
+ <td>
+ <P>The byte offset within the local name heap for the name
+ of the file. File names are stored as a URL which has a
+ protocol name, a host name, a port number, and a file
+ name:
+ <code><em>protocol</em>:<em>port</em>//<em>host</em>/<em>file</em></code>.
+ If the protocol is omitted then "file:" is assumed. If
+ the port number is omitted then a default port for that
+ protocol is used. If both the protocol and the port
+ number are omitted then the colon can also be omitted. If
+ the double slash and host name are omitted then
+ "localhost" is assumed. The file name is the only
+ mandatory part, and if the leading slash is missing then
+ it is relative to the application's current working
+ directory (the use of relative names is not
+ recommended).</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>File Offset(&lt;size&gt; bytes)</td>
+ <td>
+ <P>This is the byte offset to the start of the data in the
+ specified file. For files that contain data for a single
+ dataset this will usually be zero.</P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td>
+ <P>This is the total number of bytes reserved in the
+ specified file for raw data storage. For a file that
+ contains exactly one complete dataset which is not
+ extendable, the size will usually be the exact size of the
+ dataset. However, by making the size larger one allows
+ HDF5 to extend the dataset. The size can be set to a value
+ larger than the entire file since HDF5 will read zeros
+ past the end of the file without failing.</P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+
+ <hr>
+ <h4><a name="LayoutMessage">Name: Data Storage - Layout</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x0008</P>
+ <P class=item><B>Length:</B> varies</P>
+ <P class=item><B>Status:</B> Required for datasets, may not be repeated.</P>
+
+ <P class=item><B>Purpose and Description:</B> Data layout describes how the
+ elements of a multi-dimensional array are arranged in the linear
+ address space of the file. Three types of data layout are
+ supported:
+
+ <ol>
+ <li>Contiguous: The array can be stored in one contiguous area of the file.
+ The layout requires that the size of the array be constant and
+ does not permit chunking, compression, checksums, encryption,
+ etc. The message stores the total size of the array and the
+ offset of an element from the beginning of the storage area is
+ computed as in C.
+
+ <li>Chunked: The array domain can be regularly decomposed into chunks and
+ each chunk is allocated separately. This layout supports
+ arbitrary element traversals, compression, encryption, and
+ checksums, and the chunks can be distributed across external
+ raw data files (these features are described in other
+ messages). The message stores the size of a chunk instead of
+ the size of the entire array; the size of the entire array can
+ be calculated by traversing the B-tree that stores the chunk
+ addresses.
+
+ <li>Compact: The array can be stored in one contiguous block, as part of
+ this object header message (this is called "compact" storage below).
+ </ol>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Data Layout Message (Versions 1 and 2)
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Dimensionality</td>
+ <td>Layout Class</td>
+ <td>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Address<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension 0 (4-bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension 1 (4-bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>...</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dataset Element Size <em>(optional)</em></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Compact Data Size (4-bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Compact Data...<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>The version number information is used for changes in the format of the data
+ layout message and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by version 1.4 and before of the library to encode layout information.
+ Data space is always allocated when the data set is created.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Used by version 1.6.x of the library to encode layout information.
+ Data space is allocated only when it is necessary.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td><P>An array has a fixed dimensionality. This field
+ specifies the number of dimension size fields later in the
+ message.</P></td>
+ </tr>
+
+ <tr>
+ <td>Layout Class</td>
+ <td><P>The layout class specifies how the other fields of the
+ layout message are to be interpreted. A value of one
+ indicates contiguous storage, a value of two indicates chunked storage,
+ while a value of zero indicates compact storage. Other values will be defined
+ in the future.</P></td>
+ </tr>
+
+ <tr>
+ <td>Address</td>
+ <td><P>For contiguous storage, this is the address of the first
+ byte of storage. For chunked storage this is the address
+ of the B-tree that is used to look up the addresses of the
+ chunks. This field is not present for compact storage.
+ If the version for this message is set to 2, the address
+ may have the "undefined address" value, to indicate that
+ storage has not yet been allocated for this array.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dimensions</td>
+ <td><P>For contiguous and compact storage the dimensions define
+ the entire size of the array while for chunked storage they define
+ the size of a single chunk. In all cases, they are in units of
+ array elements (not bytes). The first dimension stored in the list
+ of dimensions is the slowest changing dimension and the last
+ dimension stored is the fastest changing dimension.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dataset Element Size</td>
+ <td><P>The size of a dataset element, in bytes. This field is only
+ present for chunked storage.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Compact Data Size</td>
+ <td><P>This field is only present for compact data storage.
+ It contains the size of the raw data for the dataset array.</P></td>
+
+ <tr>
+ <td>Compact Data</td>
+ <td><P>This field is only present for compact data storage.
+ It contains the raw data for the dataset array.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <P>Version 3 of this message re-structured the format into specific
+ properties that are required for each layout class.
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ <B>Data Layout Message (Version 3)</B>
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Layout Class</td>
+ <td colspan=2 bgcolor=#DDDDDD>&nbsp;</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Properties<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>
+ <P>The version number information is used for changes in the format of layout message
+ and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>3</code></td>
+ <td>Used by the version 1.6.3 and later of the library to store properties
+ for each layout class.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Layout Class</td>
+ <td><P>The layout class specifies how the other fields of the layout message are to be
+ interpreted. A value of one indicates contiguous storage, a value of two
+ indicates chunked storage, while a value of zero indicates compact storage.</P></td>
+ </tr>
+
+ <tr>
+ <td>Properties</td>
+ <td><P>This variable-sized field encodes information specific to each
+ layout class and is described below. If there is no property
+ information specified for a layout class, the size of this field
+ is zero bytes.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <P>Class-specific information for compact layout (Class 0): (Note: The dimensionality information
+ is in the Dataspace message)
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Size</td>
+ <td colspan=2 bgcolor=#DDDDDD>&nbsp;</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Raw Data...<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td><P>This field contains the size of the raw data for the dataset array.</P></td>
+ </tr>
+
+ <tr>
+ <td>Raw Data</td>
+ <td><P>This field contains the raw data for the dataset array.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <P>Class-specific information for contiguous layout (Class 1): (Note: The dimensionality information
+ is in the Dataspace message)
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Address<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Size<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Address</td>
+ <td><P>This is the address of the first byte of raw data storage.
+ The address may have the "undefined address" value, to indicate
+ that storage has not yet been allocated for this array.</P></td>
+ </tr>
+
+ <tr>
+ <td>Size</td>
+ <td><P>This field contains the size allocated to store the raw data.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <P>Class-specific information for chunked layout (Class 2):
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Property Descriptions
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td colspan=3 bgcolor=#DDDDDD>&nbsp;</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Address<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension 0 (4-bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dimension 1 (4-bytes)</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>...</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Dataset Element Size</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Dimensionality</td>
+ <td><P>A chunk has a fixed dimensionality. This field specifies
+ the number of dimension size fields later in the message.</P></td>
+ </tr>
+
+ <tr>
+ <td>Address</td>
+ <td><P>This is the address of the B-tree that is used to look up the addresses of the
+ chunks. The address may have the "undefined address" value, to indicate that
+ storage has not yet been allocated for this array.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dimensions</td>
+ <td><P>These values define the dimension size of a single chunk, in
+ units of array elements (not bytes). The first dimension stored in
+ the list of dimensions is the slowest changing dimension and the
+ last dimension stored is the fastest changing dimension.
+ </P>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Dataset Element Size</td>
+ <td><P>The size of a dataset element, in bytes.
+ </P>
+ </td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="ReservedMessage_0009">Name: Reserved - Not Assigned Yet</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0009</P>
+ <P class=item><B>Length:</B> N/A</P>
+ <P class=item><B>Status:</B> N/A</P>
+ <P class=item><B>Format of Data:</B> N/A</P>
+
+ <P class=item><B>Purpose and Description:</B> This message type was skipped during the initial
+ specification of the file format and may be used in a future expansion to the format.
+
+ <hr>
+ <h4><a name="ReservedMessage_000A">Name: Reserved - Not Assigned Yet</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0009</P>
+ <P class=item><B>Length:</B> N/A</P>
+ <P class=item><B>Status:</B> N/A</P>
+ <P class=item><B>Format of Data:</B> N/A</P>
+
+ <P class=item><B>Purpose and Description:</B> This message type was skipped during the initial
+ specification of the file format and may be used in a future expansion to the format.
+
+ <hr>
+ <h4><a name="FilterMessage">Name: Data Storage - Filter Pipeline</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x000B</P>
+ <P class=item><B>Length:</B> varies</P>
+ <P class=item><B>Status:</B> Optional, may not be repeated.</P>
+
+ <P class=item><B>Description:</B> This message describes the
+ filter pipeline which should be applied to the data stream by
+ providing filter identification numbers, flags, a name, and
+ client data.</P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Filter Pipeline Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Number of Filters</td>
+ <td colspan=2>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Filter List<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number for this message. This document
+ describes version 1.</P></td>
+ </tr>
+
+ <tr>
+ <td>Number of Filters</td>
+ <td><P>The total number of filters described by this
+ message. The maximum possible number of filters in a
+ message is 32.</P></td>
+ </tr>
+
+ <tr>
+ <td>Filter List</td>
+ <td><P>A description of each filter. A filter description
+ appears in the next table.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Filter Description
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=2>Filter Identification</td>
+ <td colspan=2>Name Length</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Flags</td>
+ <td colspan=2>Number of Values for Client Data</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Client Data<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Padding</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Filter Identification</td>
+ <td>
+ <p>
+ This value, often referred to as a filter identifier,
+ is designed to be a unique identifier for the filter.
+ Values from zero through 32,767 are reserved for filters
+ supported by The HDF Group in the HDF5 library and for
+ filters requested and supported by third parties.
+ Filters supported by The HDF Group are documented immediately
+ below. Information on 3rd-party filters can be found at
+ <a href="/services/contributions.html#filters">
+ <code>https://support.hdfgroup.org/services/contributions.html#filters</code></a>.
+ <a href="#Footnote1Change"><sup><small>1</small></sup></a>
+ <p>
+ To request a filter identifier, please contact
+ The HDF Group&rsquo;s Help Desk at
+ <img src="Graphics/help.png" valign="center" height=14>.
+ You will be asked to provide the following information:
+ <ol>
+ <li>Contact information for the developer requesting the
+ new identifier
+ <li>A short description of the new filter
+ <li>Links to any relevant information, including licensing
+ information
+ </ol>
+ <p>
+ Values from 32768 to 65535 are reserved for non-distributed uses
+ (for example, internal company usage) or for application usage
+ when testing a feature. The HDF Group does not track or document
+ the use of the filters with identifiers from this range.
+
+ <p>
+ The filters currently in library version 1.6.5 are
+ listed below:
+ <table class=list>
+ <tr>
+ <th width="30%">Identification</th>
+ <th align=left>Name</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>deflate</td>
+ <td>GZIP deflate compression</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>shuffle</td>
+ <td>Data element shuffling</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>3</code></td>
+ <td>fletcher32</td>
+ <td>Fletcher32 checksum</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>4</code></td>
+ <td>szip</td>
+ <td>SZIP compression</td>
+ </tr>
+ </table>
+ </P></td>
+ </tr>
+
+ <tr>
+ <td>Name Length</td>
+ <td><P>Each filter has an optional null-terminated ASCII name
+ and this field holds the length of the name including the
+ null termination padded with nulls to be a multiple of
+ eight. If the filter has no name then a value of zero is
+ stored in this field.</P></td>
+ </tr>
+
+ <tr>
+ <td>Flags</td>
+ <td><P>The flags indicate certain properties for a filter. The
+ bit values defined so far are:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>bit 1</code></td>
+ <td>If set then the filter is an optional filter.
+ During output, if an optional filter fails it will be
+ silently removed from the pipeline.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Client Data Number of Values</td>
+ <td><P>Each filter can store a few integer values to control
+ how the filter operates. The number of entries in the
+ Client Data array is stored in this field.</P></td>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td><P>If the Name Length field is non-zero then it will
+ contain the size of this field, a multiple of eight. This
+ field contains a null-terminated, ASCII character
+ string to serve as a comment/name for the filter.</P></td>
+ </tr>
+
+ <tr>
+ <td>Client Data</td>
+ <td><P>This is an array of four-byte integers which will be
+ passed to the filter function. The Client Data Number of
+ Values determines the number of elements in the array.</P></td>
+ </tr>
+
+ <tr>
+ <td>Padding</td>
+ <td><P>Four bytes of zeros are added to the message at this
+ point if the Client Data Number of Values field contains
+ an odd number.</P></td>
+ </tr>
+ </table>
+ </div>
+ <p>
+ <hr align="left" width="50">
+ <a name="Footnote1Change"><sup>1</sup></a>If you are reading
+ an earlier version of this document, this link may have changed.
+ If the link does not work, use the latest version of this document
+ on <a href="https://support.hdfgroup.org">The HDF Group</a>&rsquo;s website,
+ <a href="/HDF5/doc/H5.format.html">
+ <code>https://support.hdfgroup.org/HDF5/doc/H5.format.html</code></a>;
+ the link there will always be correct.
+ <small><a href="#FilterMessage">(Return)</a>
+ </P>
+
+ <hr>
+ <h4><a name="AttributeMessage">Name: Attribute</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x000C
+ <P class=item><B>Length:</B> varies
+ <P class=item><B>Status:</B> Optional, may be repeated.
+
+ <P class=item><B>Description:</B> The <em>Attribute</em>
+ message is used to list objects in the HDF file which are used
+ as attributes, or "metadata" about the current object. An
+ attribute is a small dataset; it has a name, a datatype, a data
+ space, and raw data. Since attributes are stored in the object
+ header they must be relatively small (<64KB) and can be
+ associated with any type of object which has an object header
+ (groups, datasets, named types and spaces, etc.).
+
+ <P class=item2>Note: Attributes on an object must have unique names. (The HDF5 library
+ currently enforces this by causing the creation of an attribute with
+ a duplicate name to fail). Attributes on different objects may have the
+ same name, however.
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Attribute Message (Version 1)
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Reserved</td>
+ <td colspan=2>Name Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Datatype Size</td>
+ <td colspan=2>Dataspace Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Datatype<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Dataspace<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Data<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number information is used for changes in the format of the
+ attribute message and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by the library before version 1.6 to encode attribute message.
+ This version does not support shared data type.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td><P>This field is reserved for later use and is set to
+ zero.</P></td>
+ </tr>
+
+ <tr>
+ <td>Name Size</td>
+ <td><P>The length of the attribute name in bytes including the
+ null terminator. Note that the Name field below may
+ contain additional padding not represented by this
+ field.</P></td>
+ </tr>
+
+ <tr>
+ <td>Datatype Size</td>
+ <td><P>The length of the datatype description in the Datatype
+ field below. Note that the Datatype field may contain
+ additional padding not represented by this field.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dataspace Size</td>
+ <td><P>The length of the dataspace description in the Dataspace
+ field below. Note that the Dataspace field may contain
+ additional padding not represented by this field.</P></td>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td><P>The null-terminated attribute name. This field is
+ padded with additional null characters to make it a
+ multiple of eight bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Datatype</td>
+ <td><P>The datatype description follows the same format as
+ described for the datatype object header message. This
+ field is padded with additional zero bytes to make it a
+ multiple of eight bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dataspace</td>
+ <td><P>The dataspace description follows the same format as
+ described for the dataspace object header message. This
+ field is padded with additional zero bytes to make it a
+ multiple of eight bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Data</td>
+ <td><P>The raw data for the attribute. The size is determined
+ from the datatype and dataspace descriptions. This
+ field is <em>not</em> padded with additional bytes.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Attribute Message (Version 2)
+ </caption>
+
+ <tr align=center>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Flag</td>
+ <td colspan=2>Name Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Type Size</td>
+ <td colspan=2>Space Size</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Name<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Type<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Space<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Data<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number information is used for changes in the format of the
+ attribute message and is described here:</P>
+ <table class=list width="90%">
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Used by the library of version 1.6.x and after to encode attribute message.
+ This version supports shared data type. The fields of name, type, and space
+ are not padded with additional bytes of zero.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Flag</td>
+ <td><P>This field indicates whether the data type of this attribute is shared:</P>
+ <table class=list width="90%">
+ <tr>
+ <th width="30%">Value</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Datatype is <em>not</em> shared.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Datatype is shared.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Name Size</td>
+ <td><P>The length of the attribute name in bytes including the
+ null terminator.</P></td>
+ </tr>
+
+ <tr>
+ <td>Datatype Size</td>
+ <td><P>The length of the datatype description in the Datatype
+ field below.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dataspace Size</td>
+ <td><P>The length of the dataspace description in the Dataspace
+ field below.</P></td>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td><P>The null-terminated attribute name. This field is <em>not</em>
+ padded with additional bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Datatype</td>
+ <td><P>The datatype description follows the same format as
+ described for the datatype object header message. This
+ field is <em>not</em> padded with additional bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Dataspace</td>
+ <td><P>The dataspace description follows the same format as
+ described for the dataspace object header message. This
+ field is <em>not</em> padded with additional bytes.</P></td>
+ </tr>
+
+ <tr>
+ <td>Data</td>
+ <td><P>The raw data for the attribute. The size is determined
+ from the datatype and dataspace descriptions. This
+ field is <em>not</em> padded with additional zero
+ bytes.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="CommentMessage">Name: Object Comment</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x000D</P>
+ <P class=item><B>Length:</B> varies</P>
+ <P class=item><B>Status:</B> Optional, may not be repeated.</P>
+
+ <P class=item><B>Description:</B> The object comment is
+ designed to be a short description of an object. An object comment
+ is a sequence of non-zero (<code>\0</code>) ASCII characters with no other
+ formatting included by the library.</P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Name Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Comment<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Name</td>
+ <td>A null terminated ASCII character string.</td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="OldModifiedMessage">Name: Object Modification Date &amp; Time (Old)</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x000E</P>
+ <P class=item><B>Length:</B> fixed</P>
+ <P class=item><B>Status:</B> Optional, may not be repeated.</P>
+
+ <P class=item><B>Description:</B> The object modification date
+ and time is a timestamp which indicates (using ISO-8601 date and
+ time format) the last modification of an object. The time is
+ updated when any object header message changes according to the
+ system clock where the change was posted.
+
+ <br><br>This modification time message is deprecated in favor of the "new"
+ modification time message (Message Type 0x0012) and is no longer written
+ to the file in versions of the HDF5 library after the 1.6.0 version.
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Modification Time Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4>Year</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Month</td>
+ <td colspan=2>Day of Month</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Hour</td>
+ <td colspan=2>Minute</td>
+ </tr>
+
+ <tr>
+ <td colspan=2>Second</td>
+ <td colspan=2>Reserved</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Year</td>
+ <td><P>The four-digit year as an ASCII string. For example,
+ <code>1998</code>. All fields of this message should be interpreted
+ as coordinated universal time (UTC)</P></td>
+ </tr>
+
+ <tr>
+ <td>Month</td>
+ <td><P>The month number as a two digit ASCII string where
+ January is <code>01</code> and December is <code>12</code>.</P></td>
+ </tr>
+
+ <tr>
+ <td>Day of Month</td>
+ <td><P>The day number within the month as a two digit ASCII
+ string. The first day of the month is <code>01</code>.</P></td>
+ </tr>
+
+ <tr>
+ <td>Hour</td>
+ <td><P>The hour of the day as a two digit ASCII string where
+ midnight is <code>00</code> and 11:00pm is <code>23</code>.</P></td>
+ </tr>
+
+ <tr>
+ <td>Minute</td>
+ <td><P>The minute of the hour as a two digit ASCII string where
+ the first minute of the hour is <code>00</code> and
+ the last is <code>59</code>.</P></td>
+ </tr>
+
+ <tr>
+ <td>Second</td>
+ <td><P>The second of the minute as a two digit ASCII string
+ where the first second of the minute is <code>00</code>
+ and the last is <code>59</code>.</P></td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td><P>This field is reserved and should always be zero.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="SharedMessage">Name: Shared Object Message</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x000F</P>
+ <P class=item><B>Length:</B> Fixed</P>
+ <P class=item><B>Status:</B> Optional, may be repeated.</P>
+
+ <P class=item><B>Description:</B> A constant message can be shared among
+ several object headers. A <em>Shared Object</em> Message contains the address of
+ the object message to be shared. Care must be exercised to prevent cycles when a
+ message of one object header points to a message in some other object header.
+ Starting from Version 2 of the Shared Object Message, the <em>Flags</em>
+ field becomes unused.
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Shared Object Message (Version 1)
+ </caption>
+
+ <tr>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Flags</td>
+ <td colspan=2>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Pointer<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number is used when there are changes in the format
+ of a shared object message and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by the library before version 1.6.1. In this version,
+ the Flags field is used to indicate whether the actual message is
+ stored in the global heap (never implemented). The Pointer field
+ either contains the the header message address in the global heap
+ (never implemented) or the address of the shared object header.</td>
+ </tr>
+ </table>
+ </tr>
+
+ <tr>
+ <td>Flags</td>
+ <td><P>The Shared Message message points to a message which is
+ shared among multiple object headers. The Flags field
+ describes the type of sharing:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Bit</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>If this bit is clear then the actual message is the
+ first message in some other object header; otherwise
+ the actual message is stored in the global heap (never
+ implemented).</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>2-7</code></td>
+ <td>Reserved (always zero)</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Pointer</td>
+ <td><P>The address of the object header
+ containing the message to be shared.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Shared Object Message (Version 2)
+ </caption>
+
+ <tr>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ <th width="25%">byte</td>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td>Flags</td>
+ <td colspan=2 bgcolor=#DDDDDD>&nbsp;</td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Pointer<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number is used when there are changes in the format
+ of a shared object message and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>2</code></td>
+ <td>Used by the library of version 1.6.1 and after. In this version,
+ The Flags field is not used and the Pointer field contains the address
+ of the object header containing the message to be shared. </td>
+ </tr>
+ </table>
+ </tr>
+
+ <tr>
+ <td>Flags</td>
+ <td><P>Unused.</P></td>
+ </tr>
+
+ <tr>
+ <td>Pointer</td>
+ <td><P>The address of the object header
+ containing the message to be shared.</P></td>
+ </tr>
+ </table>
+ </div>
+
+
+ <hr>
+ <h4><a name="ContinuationMessage">Name: Object Header Continuation</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0010</P>
+ <P class=item><B>Length:</B> fixed</P>
+ <P class=item><B>Status:</B> Optional, may be repeated.</P>
+ <P class=item><B>Description:</B> The object header continuation is the location
+ in the file of more header messages for the current data object. This can be
+ used when header blocks become too large or are likely to change over time.</P>
+
+ <P class=item><B>Format of Data:</B>
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Object Header Continuation Message
+ </caption>
+
+ <tr>
+ <th width=25%>byte</th>
+ <th width=25%>byte</th>
+ <th width=25%>byte</th>
+ <th width=25%>byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Offset<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Length<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width=30%>Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Offset</td>
+ <td><P>This value is the offset in bytes from the beginning of the file where the
+ header continuation information is located.</P></td>
+ </tr>
+
+ <tr>
+ <td>Length</td>
+ <td><P>This value is the length in bytes of the header continuation information in
+ the file.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="SymbolTableMessage">Name: Group Message</a></h4>
+ <P class=item><B>Header Message Type:</B> 0x0011</P>
+ <P class=item><B>Length:</B> fixed</P>
+ <P class=item><B>Status:</B> Required for groups, may not be repeated.</P>
+ <P class=item><B>Description:</B> Each group has a B-tree and a
+ name heap which are pointed to by this message.</P>
+ <P class=item><B>Format of data:</B>
+
+ <br>
+ <div align=center>
+ <table class=format>
+ <caption>
+ <B>Group Message</B>
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>B-tree Address<br><br></td>
+ </tr>
+
+ <tr>
+ <td colspan=4><br>Heap Address<br><br></td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width=30%>Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>B-tree Address</td>
+ <td><P>This value is the offset in bytes from the beginning of the file
+ where the B-tree is located.</P></td>
+ </tr>
+
+ <tr>
+ <td>Heap Address</td>
+ <td><P>This value is the offset in bytes from the beginning of the file
+ where the group name heap is located.</P></td>
+ </tr>
+ </table>
+ </div>
+
+ <hr>
+ <h4><a name="ModifiedMessage">Name: Object Modification Date &amp; Time</a></h4>
+
+ <P class=item><B>Header Message Type:</B> 0x0012 </P>
+ <P class=item><B>Length:</B> Fixed </P>
+ <P class=item><B>Status:</B> Optional, may not be repeated. </P>
+
+ <P class=item><B>Description:</B> The object modification date
+ and time is a timestamp which indicates the last modification of an object.
+ The time is updated when any object header message changes according to the
+ system clock where the change was posted.
+ </P>
+
+ <P class=item><B>Format of Data:</B>
+ <div align=center>
+ <table class=format>
+ <caption>
+ Modification Time Message
+ </caption>
+
+ <tr>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ <th width="25%">byte</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td colspan=3>Reserved</td>
+ </tr>
+
+ <tr>
+ <td colspan=4>Seconds After Epoch</td>
+ </tr>
+ </table>
+ </div>
+
+ <br>
+ <div align=center>
+ <table class=desc>
+ <tr>
+ <th width="30%">Field Name</th>
+ <th>Description</th>
+ </tr>
+
+ <tr>
+ <td>Version</td>
+ <td><P>The version number is used for changes in the format of Object Modification Time
+ and is described here:</P>
+ <table class=list>
+ <tr>
+ <th width="30%">Version</th>
+ <th align=left>Description</th>
+ </tr>
+
+ <tr>
+ <td align=center><code>0</code></td>
+ <td>Never used.</td>
+ </tr>
+
+ <tr>
+ <td align=center><code>1</code></td>
+ <td>Used by Version 1.6.1 and after of the library to encode time. In
+ this version, the time is the seconds after Epoch.</td>
+ </tr>
+ </table>
+ </td>
+ </tr>
+
+ <tr>
+ <td>Reserved</td>
+ <td><P>This field is reserved and should always be zero.</P></td>
+ </tr>
+
+ <tr>
+ <td>Seconds After Epoch</td>
+ <td><P>The number of seconds since 0 hours, 0 minutes, 0 seconds,
+ January 1, 1970, Coordinated Universal Time.</P></td>
+ </tr>
+ </table>
+ </div>
+
+<hr>
+<h3><a name="DataStorage">Disk Format: Level 2b - Data Object Data Storage</a></h3>
+<P>The data for an object is stored separately from the header
+information in the file and may not actually be located in the HDF5 file
+itself if the header indicates that the data is stored externally. The
+information for each record in the object is stored according to the
+dimensionality of the object (indicated in the dimensionality header message).
+Multi-dimensional data is stored in C order [same as current scheme], i.e. the
+"last" dimension changes fastest.
+<P>Data whose elements are composed of simple number-types are stored in
+native-endian IEEE format, unless they are specifically defined as being stored
+in a different machine format with the architecture-type information from the
+number-type header message. This means that each architecture will need to
+[potentially] byte-swap data values into the internal representation for that
+particular machine.
+<P> Data with a variable-length datatype is stored in the global heap
+of the HDF5 file. Global heap identifiers are stored in the
+data object storage.
+<P>Data whose elements are composed of pointer number-types are stored in several
+different ways depending on the particular pointer type involved. Simple
+pointers are just stored as the dataset offset of the object being pointed to with the
+size of the pointer being the same number of bytes as offsets in the file.
+Dataset region references are stored as a heap-ID which points to the following
+information within the file-heap: an offset of the object pointed to, number-type
+information (same format as header message), dimensionality information (same
+format as header message), sub-set start and end information (i.e. a coordinate
+location for each), and field start and end names (i.e. a [pointer to the]
+string indicating the first field included and a [pointer to the] string name
+for the last field).
+
+<P>Data of a compound datatype is stored as a contiguous stream of the items
+in the structure, with each item formatted according to its datatype.</p>
+
+<hr>
+<h3><a name="Appendix">Appendix</a></h3>
+<P>Definitions of various terms used in this document.
+</P>
+<P>The <A name="UndefinedAddress">"undefined address"</A> for a file is a
+file address with all bits set, i.e. <code>0xffff...ff</code>.
+<P>The <A name="UnlimitedDim">"unlimited size"</A> for a size is a
+value with all bits set, i.e. <code>0xffff...ff</code>.
+
+</body>
+</html>