HDF4 stands for version 4 of Hierarchical Data Format. HDF4 was originally known simply as HDF. When Version 5 was introduced, it was dubbed HDF5 to emphasize the fact that the new version was significantly different from HDF and not backwards-compatible. Later, the HDF Group decided to adopt the name HDF4 for the earlier version to avoid confusion.
At one level, HDF4 is a file format for storing scientific data. The data structure types that HDF4 supports are Scientific Data Sets, Raster Images (General, 8-bit, 24-bit APIs), color palettes, text entries, and Vdatas and Vgroups. Scientific Data Sets (SDSs) are used for storing multidimensional arrays (gridded data). Vgroups are generic grouping elements allowing a user to associate related objects within an HDF file. As Vgroups can contain other Vgroups, it is possible to build a hierarchical file. Vdatas are generic list objects. By combining Vdatas in Vgroups, it is possible to represent higher level data constructs: mesh data, multi-variate datasets, sparse matrices, finite-element data, spreadsheets, splines, non-Cartesian coordinate data, etc.
At a higher level, HDF4 is a collection of utilities and applications for manipulating, viewing, and analyzing data in HDF4 files. Between these levels, HDF4 is a software library that provides high-level APIs and a low-level data interface.
- HDF4 Documentation Latest official specification from The HDF Group.