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There are also a variety of other objects in the HDF5 Data Model that support groups and datasets, including datatypes, dataspaces, properties and attributes.


HDF5 groups (and links) organize data objects.  Every HDF5 file contains a root group that can contain other groups or be linked to objects in other files.


/foo/zoo signifies a member of the group foo, which in turn is a member of the root group.


HDF5 datasets organize and contain the “raw” data values. A dataset consists of metadata that describes the data, in addition to the data itself:


Datatypes, dataspaces, properties and (optional) attributes are HDF5 objects that describe a dataset. The datatype describes the individual data elements.

Datatypes, Dataspaces, Properties and Attributes


The datatype describes the individual data elements in a dataset. It provides complete information for data conversion to or from that datatype.      


This is an example of a dataset with a compound datatype. Each element in the dataset consists of a 16-bit integer, a character, a 32-bit integer, and a 2x3x2 array of 32-bit floats (the datatype).  It is a 2-dimensional 5 x 3 array (the dataspace). The datatype should not be confused with the dataspace.


A dataspace describes the layout of a dataset’s data elements.  It can consist of no elements (NULL), a single element (scalar), or a simple array.          


The dataspace is used to describe both the logical layout of a dataset and a subset of a dataset.


A property is a characteristic or feature of an HDF5 object. There are default properties which handle the most common needs. These default properties can be modified using the HDF5 Property List API to take advantage of more powerful or unusual features of HDF5 objects.

For example, the data storage layout property of a dataset is contiguous by default. For better performance, the layout can be modified to be chunked or chunked and compressed:



Attributes can optionally be associated with HDF5 objects. They have two parts: a name and a value. Attributes are accessed by opening the object that they are attached so are not independent objects. Typically an attribute is small in size and contains user metadata about the object that it is attached to.