+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. + +
+ ::= 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
+
+
+<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 "/" { <group_attribute>* <group_member>* }
+// Attributes and members can be in any order.
+
+<group_attribute> ::= <attribute>
+
+<attribute> ::= attribute "attr_name" { <datatype>
+ <dataspace>
+ <data>opt }
+// <datatype>, <dataspace> and <data> can be in any order
+// as long as <data> comes the last.
+
+<attr_name> ::= <identifier>
+
+<datatype> ::= datatype "<datatype_name>" ; | // shared data type
+ datatype { <scalar_datatype> } ; |
+ datatype { <dt_definition>+ } ;
+
+<datatype_name> ::= <identifier>
+
+<scalar_datatype> ::= int8 | uint8 | ... // data types supported by HDF5
+
+<dt_definition> ::= "<datatype_name>" <field_name> ; | <scalar_datatype> <field_name> ;
+
+<field_name> ::= one or more field names separated by ","
+
+<dataspace> ::= dataspace "<dataspace_name>" ; |
+ dataspace {array <current_dims> <max_dims>} ; |
+ dataspace {other <ds_definition>+ } ;
+
+<dataspace_name> ::= <identifier>
+
+<current_dims> ::= a list of integers represented of the form ( , , .. , )
+
+<max_dims> ::= a list of integers or H5S_UNLIMITED represented of the form ( , , .. , )
+
+<ds_definition> ::= TBD
+
+<data> ::= data {TBD} ;
+
+<group_member> ::= <named_datatype> | <named_dataspace> | <group> | <dataset> | <link>
+
+<named_datatype> ::= datatype "<datatype_name>" { <scalar_datatype> } |
+ datatype "<datatype_name>" { <dt_definition>+ }
+
+<named_dataspace> ::= dataspace "<dataspace_name>" {array <current_dims> <max_dims> } |
+ dataspace "<dataspace_name>" { other <ds_definition>+ }
+
+<group> ::= group "<group_name>" { <group_attribute>* <group_member>* }
+// Attributes and members can be in any order.
+
+<group_name> ::= <identifier>
+
+<dataset> ::= dataset "<dataset_name>" { <datatype>
+ <dataspace>
+ <storagelayout>opt
+ <compression>opt
+ <dataset_attribute>*
+ <data>opt }
+// Any order is ok 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> ::= a list of integers represented of the form ( , , .. , )
+
+<compact_layout> ::= TBD // not implemented yet
+
+<external_layout> ::= {external <external_file>+ }
+
+<external_file> ::= (<file_name> <offset> <size>)
+
+<offset> ::= an integer
+
+<size> ::= an integer
+
+<compression> :: = compression { TBD } ; //algorithm name and properties?
+
+<dataset_attribute> ::= <attribute> ;
+
+<link> ::= <hardlink> | <softlink>
+
+<hardlink> ::= hardlink "<hardlink_name>" { linktarget "<target>"; }
+
+<hardlink_name> ::= <identifier>
+
+<target> ::= <identifier>
+
+<softlink> ::= softlink "<softlink_name>" { linktarget "<target>"; }
+
+<softlink_name> ::= <identifier>
+
+<identifier> ::= string
+// character "/" should be used with care.
+// <dataset_name> cannot contain "/", for example.
+
+
+
+
+Consider an HDF5 file, example.h5, with the following structure:
+
+ /
+
+ / | \
+ group1 group3 dataset3
+ / \ | ^
+ group2 dataset2 hardlink --|
+ / \ ^
+ dataset1 softlink |
+ |------|
+
+
+hdf5 "example" {
+
+group "/" {
+
+ datatype "shared_datatype1" { // named data type
+ char name[20], address[40];
+ int32 id;
+ }
+
+ datatype "shared_datatype2" {
+ "shared_datatype1" rec[100];
+ float32 total;
+ }
+
+ dataspace "shared_dataspace1" { array (1000) (1000)} // named data space
+
+
+
+ attribute "group_attribute1" { //group attribute
+ datatype {int32};
+ dataspace "shared_dataspace1";
+ }
+
+ attribute "group_attribute2" {
+ datatype {int32};
+ dataspace {array (3,5) (3,5)} ;
+ data {(0,0,0,0,0) (1,1,1,1,1) (2,2,2,2,2)};
+ }
+
+
+ group "group1" {
+
+ attribute "group1_attribute" {
+ datatype {char};
+ dataspace {array (100) (200)};
+ data {("attribute_of_group_1")};
+ }
+
+ group "group2" {
+
+ datatype "shared_datatype3" {
+ int8 z;
+ int32 x;
+ }
+
+ dataset "dataset1" {
+ dataspace "shared_dataspace1";
+ datatype "shared_datatype3";
+ attribute "dataset1_attr" {
+ datatype {char};
+ dataspace {array (10) (10)};
+ data {("data1")};
+ };
+ }
+
+
+ softlink "sl" {
+ linktarget "/group1/dataset2";
+ }
+ }
+
+ dataset "dataset2" {
+ datatype {int8};
+ dataspace {array (2,5) (unlimited, 5)};
+ data {(0,0,0,0,0) (0,0,0,0,0)};
+ }
+ }
+
+ group "group3" {
+ hardlink "hl" {
+ linktarget "/dataset3" ;
+ }
+ }
+
+
+ dataset "dataset3" {
+ datatype { float32 };
+ dataspace {array (1000,1000) (1000,1000) };
+ storagelayout {chunked (250,1000)};
+ }
+
+} // root group
+
+}