A data structure that stores
meta-data, i.e. data
about
data. The term "data dictionary" has several uses.
Most generally it is a set of data descriptions that
can be shared by several applications.
Usually it means a
table in a
database that stores the
names,
field types, length, and other characteristics of
the fields in the database tables.
An active data dictionary is automatically updated as changes
occur in the database. A passive data dictionary must be
manually updated.
In a
DBMS, this functionality is performed by the
system catalog. The data dictionary is a more general software
utility used by designers, users, and administrators for
information resource management.
The data dictionary may maintain information on system
hardware, software, documentation, users, and other aspects.
Data dictionaries are also used to document the database
design process itself and can accumulate meta-data
ready to feed into the system catalog.