Data Dictionary Storage

Data Dictionary Storage

• Definition:Data dictionary is mini database management system that manages the metadata.

• Data dictionaries are helpful to the database administrators in management of database.

• The general structure of data dictionary is as shown in the Fig. 4.4.1.

• The data in the database dictionary is maintained by several programs and generates the reports if required.

• The data dictionary is integrated with the database systems in which the data is controlled by the data dictionaries and is made available to the DBMS software.

• Following type of information is maintained by data dictionary -

a) Description of the schema of the database.

b) Detailed information about the physical database design.

c) Description of database users, their roles and their access rights.

d) Description of database transactions.

e) The description of the relationship between database transactions and data items referenced by them.

f) Information about the usage statistics. That means, how many times the queries are raised to the database, how many transactions are made by the DBMS.

• For example - Consider a Student database, in which various fields are RollNo, FirstName, LastName, and CourseID. The data dictionary for this database ban maintains the information about this database. The data dictionary contains the dog column names, Data type of each field and the description of each column of the database.

Active and Passive Data Dictionaries

Active data dictionary

• Active Data dictionary is managed automatically by the database management system.

• They are consistent with current structure.

• In the active data dictionary, when any modification or changes is executed by the DBMS, then this dictionary it also gets modified by the DBMS automatically.

• Most of the active data dictionaries are derived from system catalog.

Passive data dictionary                        

• Passive data dictionary is used only for documentation purpose.

• Passive dictionary is a self-contained application and set of files used for documenting the data processing environment.

• The process of maintaining or modification of the database is manual.

• It is managed by the users of the database systems.

Difference between active and passive data dictionary