• A DBMS needs to maintain a description of all the data items that it contains. Like a RDBMS contains information about all relation, databse objects, views and index present in it.

• The DBMS should also maintains information about views (a definition of the view) to compute the tuples that belong in the view whenever the view is queried or called.

• The multiple relations which stores information about data in database. Such tuples are created and maintained by the system itself. They are called as Catalog relations.

• The catalog relations are also called the system catalog or the data dictionary.

• The system catalog is sometimes also referred to as metadata (data about data).

• The information in the system catalog is generally used only for query optimization.

Relation:

1) Name of the given relation.

2) Name of attribute and type of attributes of relation.

3) Index name for all indexes on the relation.

4) Integrity constraints imposed on the relation.

Index:

1) Name of index and structure of the index(e.g.,hash index)

2) Search key attributes.

View:

1) Name of view name

2) View definition.