What is Systen Catalogue in DBMS ?

System Catalogue : A repository of information describing the data in the database, that is the meta-data or data about data.

Data Dictionary (also called system catalogue) stores meta-data that is, data about data, such as :

Information about relations

• Names of relations.
• Names and Types of attributes of each relation.
• Names and Definitions of views.
• Integrity constraints. 

User and accounting information, including passwords.

• Names of authorized users.
• Accounting information about users.
• Passwords or other information used to authenticate Statistical and Descriptive data.
• Number of tuples in each relation.
• Method of storage for each relation.

Physical file organization information.

• How relation is stored (sequential/hash/...).

• Physical location of relation.

   (a) Operating system file name or

   (b) Disk addresses of blocks containing records of the relation.

Information about indices.

• Name of the index.
• Name of relation being indexed.
• Attributes on which the index is defined.
• Types of index formed.

Catalog structure can use either specialized data structures designed for efficient access or a set of relations, with existing system features used to ensure efficient access.

A Possible Catalogue Representation : primary keys are underlined

Relation-meta-data = (relation-name, name-of-attributes, storage-organization, location)
Attribute-meta-data = (attribute-name, relation-name, domain-type, position, length)
User-meta-data = (user-name, encrypted-password, group)
Index-meta-data = (index-name, relation-name, index-type, index-attributes)
View-meta-data = (view-name, definition)