The C Interfaces:
The Datatype interface, H5T, provides a mechanism to describe the storage format of individual data points of a data set and is hopefully designed in such a way as to allow new features to be easily added without disrupting applications that use the data type interface. A dataset (the H5D interface) is composed of a collection or raw data points of homogeneous type organized according to the data space (the H5S interface).
A datatype is a collection of datatype properties, all of which can be stored on disk, and which when taken as a whole, provide complete information for data conversion to or from that datatype. The interface provides functions to set and query properties of a datatype.
A data point is an instance of a datatype, which is an instance of a type class. We have defined a set of type classes and properties which can be extended at a later time. The atomic type classes are those which describe types which cannot be decomposed at the datatype interface level; all other classes are compound.
See “HDF5 Datatypes” in the HDF5 User’s Guide for more information.