What is the data Dictionary or metadata in DBMS?

A Data Dictionary is an integral part of a database. It holds the information about the database and the data that it stores called as metadata.

• A meta data is the data about the data.

• It is the self-describing nature of databases.

• It holds the information about each data element in the database.

• Such as names, types, range of values, access authorization, indicate which application program uses the data.

• Meta data is used by the developers to develop the program, queries to manage and manipulate the data.

Types of dictionaries

In general, DBMS data dictionaries are of two types. These dictionaries are as follows −

Active data dictionary

• It is managed automatically by the data management software.

• It is always consistent with the current structure of the database.

Passive data dictionary

• It is mainly used for documentation purposes.

• It is managed by the user of the system and is modified manually by the user.

The data dictionaries are pictorially represented as follows −

Data in DBMS data dictionary

The data in DBMS data dictionary is explained below −

Schema

• Tables

• Columns

• Constraints

• Foreign keys

• Indexes

• Sequences

Programs

• Views

• User defined functions

• Stored procedures

• Triggers

Security

• Users

• User groups

• Privileges

Physical implementation

• Partitions

• Files

• Backups

Storage

• Size of tables and indexes in KBs

• Number of rows in tables