What is Data Dictionary in DBMS
What is Data dictionary in DBMS: The data dictionary is also referred as data repository or system catalog. It is an important part of DBMS. It contains data about data. It means that the data dictionary contains the actual database description managed by DBMS. Data dictionary is automatically updated as data is inserted and updated with the passage of time. The data dictionary contains the following information
- Logical structure of database such as table name, column name of each table and their data types and other properties, indices created in a table, and stored procedure name etc.
- Schemas, mapping and constraints.
- Description about application program.
- Description about physical database design such as storage structure, access path etc.
- Description about users of DBMS and their access rights.
- It also keeps record of accessing the database
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There are different types of data dictionaries. The main type of data dictionaries are described below.
- Integrated Data Dictionary
- Freestanding Data Dictionary
Integrated Data Dictionary
Data dictionary which is a part of DBMS is referred as Integrated Data Dictionary. In most DBMSs the data dictionary is integrated and active. The DBMS checks this type of data dictionary every time the database is accessed.
Freestanding Data Dictionary
A data dictionary that is separated part of DBMS is referred to as Freestanding Data Dictionary. It may be a commercial product or a simple file developed and maintained by a database designer. The freestanding data dictionary is useful in the initial stage of design for collecting and organizing information about data.