The data dictionary (in a database management system) is a set of records which store definitions of the data elements, characteristics, and structure. It contains details of tables, indexes, columns, data types, views, and other database objects.
The Data Dictionary serves the following roles-
- Reference map to the DBMS
When the DBMS is processing a DML query it needs to look up the data dictionary to find the various tables, the columns, to check the data type and storage buffer and validate it, before proceeding further. The data dictionary acts as an index, a map, and a reference guide.
- Design document
The data dictionary serves as a design document to the DBA. It helps the DBA to be able to see an overview of the structure of the database, data sources, and aids in maintenance and redesign.
- DBMS health tool
The data dictionary is a standardization mechanism and is used to manage controls, scheduling, and in keeping a check on the health of the database. It allows the DBA to identify “organizational data irregularity”.
- Report facility
Provides as input to reports on “impact analysis”.
- Corporate glossary
Acts as the “corporate glossary” of a dynamically growing information resource.