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The HDF5 specification defines the standard objects and storage for the standard HDF5 objects. (For information about the HDF5 library, model and specification, see the HDF documentation.)  This document is an additional specification do define a standard profile for how to store tables in HDF5. Table data in HDF5 is stored as HDF5 datasets with standard attributes to define the properties of the tables.

1. Overview

A generic table is a sequence of records, each record has a name and a type. Table data is stored as an HDF5 one dimensional compound dataset.  A table is defined as a collection of records whose values are stored in fixed-length fields. All records have the same structure and all values in each field have the same data type.

The dataset for a table is distinguished from other datasets by giving it an attribute "CLASS=TABLE".   Optional attributes allow the storage of a title for the Table and for each column, and a fill value for each column.

2.  Table Attributes

The attributes for the Table are strings. They are written with the H5LTset_attribute_string Lite API function.  "Required" attributes must always be used. "Optional" attributes must be used when required.   

Attributes

Attribute name="CLASS" (Required)

This attribute is type H5T_C_S1, with size 5.
For all Tables, the value of this attribute is "TABLE".
This attribute identifies this data set as intended to be interpreted as Table that conforms to the specifications on this page.

Attribute name="VERSION" (Required)

This attribute is of type H5T_C_S1, with size corresponding to the length of the version string.  This attribute identifies the version number of this specification to which it conforms.  The current version number is "0.2".

Attribute name="TITLE" (Optional)

The TITLE is an optional String that is to be used as the informative title of the whole table. The TITLE is set with the parameter table_title of the function H5TBmake_table

Attribute name="FIELD_(n)_NAME" (Required)

The FIELD_(n)_NAME is an optional String that is to be used as the informative title of column n of the table. For each of the fields the word FIELD_ is concatenated with the zero based field (n) index together with the name of the field.

Attribute name="FIELD_(n)_FILL" (Optional)

The FIELD_(n)_FILL is an optional String that is the fill value for column n of the table. For each of the fields the word FIELD_ is concatenated with the zero based field (n) index together with the fill value, if present. This value is written only when a fill value is defined for the table.

 

Table 1. Attributes of an Image Dataset Attribute Name (R = Required 

Attribute Name(R = Required 
O= Optional)
TypeString SizeValue
CLASSRString5"TABLE"
VERSIONRString3"0.2"
TITLEOString  
FIELD_(n)_NAMERString  
FIELD_(n)_FILLO*String  

The attribute FIELD_(n)_FILL is written to the table if a fill value is specified on the creation of the Table. Otherwise, it is not.

The following section of code shows the calls necessary to the creation of a table.

/* Create a new HDF5 file using default properties. */
file_id = H5Fcreate( "my_table.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT );
/* Call the make table function */
H5TBmake_table( "Table Title", file_id, "Table1", NFIELDS, NRECORDS, dst_size, 
field_names, dst_offset, field_type, 
chunk_size, fill_data, compress, p_data )
/* Close the file. */
status = H5Fclose( file_id );

For more information see the “H5TB: HDF5 Table” reference manual page and the HDF5 Tutorial, which includes and examples.

--- Last Modified: August 22, 2017 | 04:23 PM