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Hierarchical Data Format (HDF) is a family of formats and supporting software for storing and organizing data. HDF5 is a specific, current-generation format in that family: it combines a file format, a model for organizing data, and software libraries, language interfaces, and tools for using it. An HDF5 file can hold named groups and multidimensional datasets, with datatypes, dataspaces, links, and descriptive attributes explaining how its contents are organized.
What does “hierarchical data format” mean?
HDF is the broader name for a family of data formats and software. HDF5 is one specific format and software system in that family. The name can be misleading if it suggests only a file extension: HDF5 also defines a logical data model and provides software for applications to create, organize, read, and write HDF5 data.
The HDF Group describes HDF5 as a file format, a model for logically organizing and accessing data, and the software used to work with it. Its files can store heterogeneous kinds of information, including data represented as images, tables, graphs, or documents. The HDF Group’s HDF5 introduction outlines these roles.
How is information organized in an HDF5 file?
HDF5’s model uses groups to organize named objects and datasets to hold array data. Datatypes and dataspaces describe the elements and shape of a dataset; attributes attach descriptive information to objects. Links connect names to objects. The HDF5 guide includes these concepts as well as files and property lists; the Open Geospatial Consortium’s HDF5 Core Standard enumerates six core entities: Group, Dataset, Link, Datatype, Dataspace, and Attribute.
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Groups and links
A group is a container, much like a directory in a file system. Groups and paths make it convenient to navigate an HDF5 file, but the underlying organization should not be understood as only a simple directory tree. Links connect names and objects, so the model can be graph-like rather than strictly hierarchical.
Datasets, datatypes, and dataspaces
A dataset stores a multidimensional rectangular array. Its datatype defines the representation and interpretation of its elements, while its dataspace describes the array’s rank and dimensions. Together, these concepts distinguish the stored values from the structure and meaning needed to interpret them.
Attributes
An attribute is named descriptive data associated with a group, dataset, or named datatype. The HDF5 guide recommends keeping attributes small because each attribute is accessed as a whole in a single read or write operation. The HDF5 Data Model and File Structure guide explains these model elements.
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The groups, datasets, and other objects that an application sees are represented by lower-level structures in the stored file. The file-format specification describes elements such as superblocks, object headers, B-trees, heaps, and object data. These implementation details explain how the logical model is encoded; they are not additional kinds of user-facing content that must be organized manually. See The HDF5 File Format Specification for the storage-level description.
What is HDF5 used for?
HDF5 is intended to manage, process, and store heterogeneous data, including n-dimensional datasets. The documented workflows include creating files, creating and writing datasets, reading data, and reading portions of datasets. Whether a particular application supports those workflows depends on its own implementation; the format’s capabilities alone do not guarantee a particular performance outcome. The HDF5 User Guide covers programming and file operations, and The HDF5 Library & File Format overview describes the library and format.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is HDF the same as HDF5?
No. HDF is the family name; HDF5 is a particular format and software system with its own data model and file specification. The shared name does not mean that HDF5 and earlier HDF formats are interchangeable. The sources cited here do not establish detailed compatibility or migration behavior, so those questions should be checked against the documentation for the specific versions and software involved.
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