system catalog <database> The {data dictionary} of a {DBMS}. The system catalogue stores {meta-data} including the {schemas} of the {databases}. It is a mini-database, and is usually stored using the DBMS itself in special {tables} called {system tables}. It maybe referred to as being "on line", as it is active, and can be queried by users like any other table. (1999-04-27)