doc/html/ddl.html


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<html>

<head>
<TITLE>DDL for HDF5</TITLE>
</head>

<body>

<B> DDL in BNF  </B> <br>

<P>
The following describes the data description language for HDF5 file. 
The description is in Backus-Naur Form.  A quick explanation
of the some symbols used.

<PRE>
	::=               defined as
	&lt;tname&gt;           a token with the name tname
	&lt;a&gt; | &lt;b&gt;         one of &lt;a&gt; or &lt;b&gt;
	&lt;a&gt;<FONT SIZE=1.7>opt</FONT>             zero or one occurrence of &lt;a&gt;
	&lt;a&gt;*              zero or more occurrence of &lt;a&gt;
	&lt;a&gt;+              one or more occurrence of &lt;a&gt;
        TBD               To Be Decided


&lt;file&gt; ::= hdf5 "&lt;file_name&gt;" { &lt;file_boot_block&gt;<FONT SIZE=1.7>opt</FONT> &lt;root_group&gt; }

&lt;file_name&gt; ::= &lt;identifier&gt;

&lt;file_boot_block&gt; ::= boot_block { &lt;boot_block_content&gt; }

&lt;boot_block_content&gt; ::= TBD

&lt;root_group&gt; ::= group "/" { &lt;nlink&gt;<FONT SIZE=1.7>opt</FONT> &lt;group_attribute&gt;* &lt;group_member&gt;* }  
// nlink must appear before attributes and members.

&lt;nlink&gt;<FONT SIZE=1.7>opt</FONT> ::= { nlink &lt;no_of_hardlinks&gt; }

&lt;no_of_hardlinks&gt; ::= an integer larger than 1

&lt;group_attribute&gt; ::= &lt;attribute&gt; 

&lt;attribute&gt; ::= attribute "attr_name" { &lt;datatype&gt;    
                                        &lt;dataspace&gt;   
                                        &lt;data&gt;<FONT SIZE=1.7>opt</FONT>  } 
// &lt;datatype&gt;, &lt;dataspace&gt; and &lt;data&gt; can be in any order 
// as long as &lt;data&gt; comes the last.

&lt;attr_name&gt; ::=  &lt;identifier&gt;

&lt;datatype&gt; ::= datatype { "&lt;datatype_name&gt;" } |          // shared data type
               datatype { &lt;scalar_datatype&gt; }  |         
               datatype { &lt;dt_definition&gt;+ }        

&lt;datatype_name&gt; ::= &lt;identifier&gt;

&lt;scalar_datatype&gt; ::= H5T_NATIVE_CHAR | H5T_NATIVE_INT | ...     // data types supported by HDF5

&lt;dt_definition&gt; ::= &lt;scalar_datatype&gt; &lt;field_name&gt; ;

&lt;field_name&gt; ::= &lt;identifier&gt;

&lt;dataspace&gt; ::= dataspace { "&lt;dataspace_name&gt;" } |
                dataspace { array &lt;current_dims&gt; &lt;max_dims&gt; } | 
                dataspace { other &lt;ds_definition&gt;+ } 

&lt;dataspace_name&gt; ::= &lt;identifier&gt;

&lt;current_dims&gt; ::= a list of integers represented as (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ) where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,...

&lt;max_dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ) where <i>i<FONT SIZE=1.0>k</i></FONT> is an integer or H5S_UNLIMITED

&lt;ds_definition&gt; ::= TBD

&lt;data&gt; ::= data {TBD}

&lt;group_member&gt; ::= &lt;named_datatype&gt; | &lt;named_dataspace&gt; | &lt;group&gt; | &lt;dataset&gt; | &lt;softlink&gt;

&lt;named_datatype&gt; ::= datatype "&lt;datatype_name&gt;" { &lt;dt_definition&gt;+ }

&lt;named_dataspace&gt; ::= dataspace "&lt;dataspace_name&gt;" { array &lt;current_dims&gt; &lt;max_dims&gt; } |
                      dataspace "&lt;dataspace_name&gt;" { other &lt;ds_definition&gt;+ }

&lt;group&gt; ::= group "&lt;group_name&gt;" { &lt;nlink&gt;<FONT SIZE=1.7>opt</FONT> &lt;group_attribute&gt;* &lt;group_member&gt;* }  

&lt;group_name&gt; ::= &lt;identifier&gt;

&lt;dataset&gt; ::= dataset "&lt;dataset_name&gt;" { &lt;nlink&gt;<FONT SIZE=1.7>opt</FONT>
                                         &lt;datatype&gt;  
                                         &lt;dataspace&gt; 
                                         &lt;storagelayout&gt;<FONT SIZE=1.7>opt</FONT>
                                         &lt;compression&gt;<FONT SIZE=1.7>opt</FONT>
                                         &lt;dataset_attribute&gt;*
                                         &lt;data&gt;<FONT SIZE=1.7>opt</FONT>  } 
// Any order is ok as long as &lt;data&gt; and &lt;dataset_attribute&gt; are 
// after &lt;datatype&gt; and &lt;dataspace&gt;.
// nlink must appear before others.

&lt;dataset_name&gt; ::= &lt;identifier&gt;

&lt;storagelayout&gt; :: = storagelayout &lt;contiguous_layout&gt;  |  
                     storagelayout &lt;chunked_layout&gt;  | 
                     storagelayout &lt;compact_layout&gt;  | 
                     storagelayout &lt;external_layout&gt; 

&lt;contiguous_layout&gt; ::= {contiguous}    // default

&lt;chunked_layout&gt; ::=  {chunked &lt;dims&gt; }

&lt;dims&gt; ::= (<i>i<FONT SIZE=1.0>1</i></FONT>, <i>i<FONT SIZE=1.0>2</i></FONT>, ... ), <i>i<FONT SIZE=1.0>k</i></FONT> is an integer, <i>k</i> = 1,2,... 

&lt;compact_layout&gt; ::= TBD           

&lt;external_layout&gt; ::= {external &lt;external_file&gt;+ }

&lt;external_file&gt; ::= (&lt;file_name&gt; &lt;offset&gt; &lt;size&gt;) 

&lt;offset&gt; ::= an integer

&lt;size&gt; ::= an integer

&lt;compression&gt; :: = compression { TBD }  

&lt;dataset_attribute&gt; ::= &lt;attribute&gt; 

&lt;softlink&gt; ::= softlink "&lt;softlink_name&gt;" { linktarget "&lt;target&gt;" }

&lt;softlink_name&gt; ::= &lt;identifier&gt;

&lt;target&gt; ::= &lt;identifier&gt;

&lt;identifier&gt; ::= string   
// character "/" should be used with care. 
// &lt;dataset_name&gt; cannot contain "/", for example.

</PRE>
<HR>
<B> An example of HDF5 File in DDL </B>
<PRE>

Consider an HDF5 file, example.h5, with the following structure:

                             /

                     /       |       \
                 group1     group3  dataset3
                 /   \       |       
           group2  dataset2 softlink
             /
      dataset1 
              

hdf5 "example" { 

group "/" {

   datatype "shared_datatype" {                    // named data type
            H5T_NATIVE_CHAR c[20];
            H5T_NATIVE_INT i; 
   }
 
   attribute "group_attribute" {                   //attribute
             datatype {H5T_NATIVE_CHAR}
             dataspace {array (20) (20)}
             data { "group attribute" }
   } 

   group "group1" {

         group "group2" {

               dataset "dataset1" {
                        dataspace {array (4) (4)}
                        datatype {"shared_datatype"}
                        attribute "dataset1_attr" {
                                   datatype {H5T_NATIVE_CHAR}
                                   dataspace {array (10) (10)}
                        }
               }
         }

         dataset "dataset2" {
               datatype {H5T_NATIVE_INT}
               dataspace {array (2,5) (H5S_UNLIMITED, 5)}
               data {0,0,0,0,0,0,0,0,0,0}
         }
   }
   
   group "group3" {
         softlink "slink" {
                  linktarget "/sometarget" 
         }
   }
      
   
   dataset "dataset3" {
           datatype {H5T_NATIVE_FLOAT}
           dataspace {array (100,100) (100,100)} 
   }
 
} 

}