A
data dictionary, or
metadata repository, as defined in the
IBM Dictionary of Computing, is a "centralized repository of information about data such as meaning, relationships to other data, origin, usage, and format. " The term may have one of several closely related meanings pertaining to
databases and
database management systems (DBMS):
a
document describing a database or collection of databases
an integral
component of a
DBMS that is required to determine its structure
a piece of
middleware that extends or supplants the native data dictionary of a DBMS