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2.2 The Hierarchy of HDF Interaction
To review the description of HDF provided in Chapter 1, HDF is a physical file format at its lowest level and a collection of utilities and applications at its highest. Between these two levels, HDF is a library that itself provides two levels of programming interfaces. HDF can be thought of conceptually as three interface layers built upon a physical file format.
FIGURE 2a The Three Levels of Interaction with the HDF File Format
Refer to Figure 2a. Of the three types of top-level general applications, only the command-line utilities will be extensively covered in this manual. See Chapter 13, titled HDF Command-Line Utilities, for descriptions of this aspect of HDF. These general applications directly call the single-file and multifile interfaces.
The two interactive levels immediately below this level, the low-level interface and the HDF data file itself, are only briefly described as the single-file and multifile interfaces provide a safer and more standardized means of accessing these levels. The single-file and multifile interfaces - the second highest level of interaction within HDF - are routinely updated as aspects of these lower-level interfaces are changed, in a manner as transparent to the HDF user as possible. With the exception of the few instances where lower-level interface functionality has not yet been incorporated into the higher-level interface functions, the HDF user need not directly concern themselves with these levels.
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HDF User's Guide - 06/04/97, NCSA HDF
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