The System Catalog Describing the Data Copyright © Curt Hill 2003-2008 Describe the tables of metadata Copyright © Curt Hill 2003-2008
What does a DBMS Store? Obviously: the data of the relations Less obviously: Relation formats Field attributes Index formats Metadata: descriptions of how the data is stored Copyright © Curt Hill 2003-2008
Table Metadata Table Name – used in SQL File name – internally used Fields Name Type Other attributes – such as unique Index names on this table Any contraints Integrity Referential Copyright © Curt Hill 2003-2008
Other Metadata Index Users View Name Structure type Names Passwords B+Tree Hash Users Names Passwords Authority View Description Copyright © Curt Hill 2003-2008
Statistics Statistical data may also be stored in the system catalog This does not have to be updated at every change Which could impede performance Must be periodically updated Data could include for either tables or indexes: Size in terms of records and pages Range and height for tree index Copyright © Curt Hill 2003-2008
Storage The system catalog is merely a set of relations Hence it is a database Manipulated with normal means with some special privileges Each DBMS may use different tables with different names The login procedure then becomes a stored procedure Take a user ID and password Plug into a query Find the security attributes If there are none then the user is invalid Copyright © Curt Hill 2003-2008