DDL in BNF for HDF5

1. Introduction

This document contains the data description language (DDL) for an HDF5 file. The description is in Backus-Naur Form.

2. Explanation of Symbols

This section contains a brief explanation of the symbols used in the DDL.

    ::=                      defined as
    <tname>                  a token with the name tname
    <a> | <b>                one of <a> or <b>
    <a>opt                    zero or one occurrence of <a>
    <a>*                     zero or more occurrence of <a>
    <a>+                     one or more occurrence of <a>
    TBD                      To Be Decided

3. The DDL

<file> ::= HDF5 "<file_name>" { <file_boot_block>opt <root_group> }

<file_name> ::= <identifier>

<file_boot_block> ::= BOOT_BLOCK { <boot_block_content> }

<boot_block_content> ::= TBD

<root_group> ::= GROUP "/" { <unamed_datatype>* <group_attribute>* <group_member>* }  

<unamed_datatype> ::= DATATYPE "<unamed_type_name>" { <compound_type_def>+ }

<unamed_type_name> ::= the assigned name for unamed type is in the form of 
                      #oid1:oid2, where oid1 and oid2 are the object ids of the type

<compound_type_def> ::=  <named_scalar_type> | <named_array_type>

<named_scalar_type> ::= <scalar_type> <field_name> ;

<scalar_type> ::= H5T_STD_I8BE | H5T_STD_I8LE | ...

<field_name> ::= <identifier>

<named_array_type> ::= <scalar_type> <field_name> <dim_sizes> ;

<dim_sizes> ::= dimension sizes in the form of [dimsize1][dimzise2]..., 
                where dimsize1, dimsize2 are integers

<group_attribute> ::= <attribute> 

<attribute> ::= ATTRIBUTE "<attr_name>" { <datatype>    
                                          <dataspace>   
                                          <data>opt  } 
// <datatype> and <dataspace> must appear before <data>.

<attr_name> ::=  <identifier>

<datatype> ::= DATATYPE { <named_type> } |        
               DATATYPE { "<scalar_type>" }  |         
               DATATYPE { <compound_type_def>+ }

<named_type> ::= <hardlink>

<hardlink> ::= HARDLINK { "<abs_name>" }  

<abs_name> ::= object absolute name

<dataspace> ::= DATASPACE { "<dataspace_name>" } |
                DATASPACE { ARRAY <current_dims> <max_dims> } | 
                DATASPACE { OTHER <ds_definition>+ } 

<dataspace_name> ::= <identifier>

<current_dims> ::= a list of integers in the form of (i1, i2, ... ),
                   where ik is an integer, k = 1,2,...

<max_dims> ::= (i1, i2, ... ) where ik is an integer or H5S_UNLIMITED

<ds_definition> ::= TBD

<data> ::= data {TBD}

<group_member> ::= <named_datatype> | <named_dataspace> | <group> | <dataset> | 
                   <softlink>

<named_datatype> ::= DATATYPE "<type_name>" { <compound_type_def>+ }

<type_name> ::= "<identifier>"

<named_dataspace> ::= DATASPACE "<dataspace_name>" { ARRAY <current_dims> <max_dims> } |
                      DATASPACE "<dataspace_name>" { OTHER <ds_definition>+ }

<group> ::= GROUP "<group_name>" { <hardlink> } |
            GROUP "<group_name>" { <group_attribute>* <group_member>* } 
            
<group_name> ::= <identifier>

<dataset> ::= DATASET "<dataset_name>" { <hardlink> } |
              DATASET "<dataset_name>" { <datatype>  
                                         <dataspace> 
                                         <storagelayout>opt
                                         <compression>opt
                                         <dataset_attribute>*
                                         <data>opt  } 
// Tokens within {} can be in any order  as long as <data> and <dataset_attribute>
// are after <datatype> and <dataspace>.

<dataset_name> ::= <identifier>

<storagelayout> :: = STORAGELAYOUT <contiguous_layout>  |  
                     STORAGELAYOUT <chunked_layout>  | 
                     STORAGELAYOUT <compact_layout>  | 
                     STORAGELAYOUT <external_layout> 

<contiguous_layout> ::= {CONTIGUOUS}    // default

<chunked_layout> ::=  {CHUNKED <dims> }

<dims> ::= (i1, i2, ... ), ik is an integer, k = 1,2,... 

<compact_layout> ::= TBD           

<external_layout> ::= {EXTERNAL <external_file>+ }

<external_file> ::= (<file_name> <offset> <size>) 

<offset> ::= an integer

<size> ::= an integer

<compression> :: = COMPRESSION { TBD }  

<dataset_attribute> ::= <attribute> 

<softlink> ::= SOFTLINK "<softlink_name>" { LINKTARGET "<target>" }

<softlink_name> ::= <identifier>

<target> ::= <identifier>

<identifier> ::= string   
// character '/' should be used with care.

4. An Example of an HDF5 File in DDL

HDF5 "example.h5" {
GROUP "/" {
   DATASET "dset1" {
      DATATYPE {
         H5T_STD_I32BE int_name;
         H5T_IEEE_F32BE float_name;
         H5T_IEEE_F64BE double_name;
      }
      DATASPACE { ARRAY ( 5 ) ( 5 ) }
      DATA {{0,0,1}, {1,1,0.5}, {2,4,0.333333}, {3,9,0.25}, {4,16,0.2}}
   }
   GROUP "group1" {
      DATASET "dset2" {
         DATATYPE {
            HARDLINK { "/type1" }
         }
         DATASPACE { ARRAY ( 5 ) ( 5 ) }
         DATA {{0,0}, {1,1.1}, {2,2.2}, {3,3.3}, {4,4.4}}
      }
   }
   GROUP "group2" {
      HARDLINK { "/group1" }
   }
   SOFTLINK "slink1" {
      LINKTARGET "somevalue"
   }
   DATATYPE "type1" {
      H5T_STD_I32BE int_name;
      H5T_IEEE_F32BE float_name;
   }
}
}

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Last modified: 28 October 1998