Each data file in memory or on disk has an associated dictionary, whose primary purpose is to describe the data in the file. See Variables, for a PSPP user's view of a dictionary.
A data file stored in a PSPP format, either as a system or portable file, has a representation of its dictionary embedded in it. Other kinds of data files are usually not self-describing enough to construct a dictionary unassisted, so the dictionaries for these files must be specified explicitly with PSPP commands such as DATA LIST.
The most important content of a dictionary is an array of variables, which must have unique names. A dictionary also conceptually contains a mapping from each of its variables to a location within a case (see Cases), although in fact these mappings are stored within individual variables.
System variables are not members of any dictionary (see System Variables).
Dictionaries are represented by
struct dictionary. Declarations
related to dictionaries are in the <data/dictionary.h> header.
The following sections describe functions for use with dictionaries.