Data Dictionary (data dictionary/directory; DD/D)
Definition/Meaning:
A structured description of a
database. It contains descriptions of the entities in the database, as distinct
from the raw data held in the database itself. A basic data dictionary will
contain the various schemes that apply to the database, information on the
mapping of the database onto physical storage, data validation rules, and rules
used to check for authorized access to the database. This basic information
concerning the database is sometimes termed a directory. A more comprehensive
data dictionary will also include cross-reference information, showing, for
example, which programs access which data or which departments within an
organization receive which reports.
Because it contains all pertinent
information on the nature of the data in the database and its use, the data
dictionary is of vital importance in a complete database system. It allows the
database administrator to retain overall control of a database that is evolving
and is accessed by a changing set of programs. Since the data dictionary is
itself normally treated as a database, it can be regarded as a database about a
database.
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