Data Dictionary-

In DBMS data dictionary is play key role in DBMS. Data dictionary is a metadata about all data and transaction in DBMS. In data dictionary stores the all information about data and their attribute information. Data dictionary is important for describing all data information like where from data comes and hows they work in DBMS system.In data dictionary store all information about database is called metadata about that database system mainly. In metadata or in data dictionary stores fallowing information about data-

1. Table names and their relationships between other tables mainly.
2. Column relationships with another tables.
3. Constraints information about all tables.
4. Key formations about each tables like primary key and foreign key.
5. Last accessed information about table.
6. Last updated information about table.
7. Attribute information about each table and its values.

There is 2 types of data dictionary mainly-

1. Active Data Dictionary-

That dictionary updated automatically from software used for DBMS system

2. passive Data Dictionary-

Managed by user if in database some change occurred. it is also called as non-integrated data dictionary.