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)