What is a data dictionary, its purpose?

A data dictionary is a file or an assemblage of files that contain a database’s metadata. It will contain records about other objects in the database, such as data control, data connections to other objects, and other data. This is the central component of any relational database. It is invisible to most database users. Only database administrators interact with the data dictionary.

Web programs use the certain types data model to build the web development, a data dictionary can be discussed to know where a data item fits in the structure, what values it may contain, and fundamentally what the data item means in real-world terms. For example, a college or group of colleges could model the data objects involved in offering multiple courses. Then they could provide a data dictionary for programmers. The data dictionary would describe each of the data items in its data model for several courses.

The Logical Entity Relationship or conceptual diagram will concentrate on the high-level business notions, a Data Dictionary will give more detail about each and every trait of a business concept.

The Purpose of data dictionaries are

  • It describes the data objects of each user in the database. By this means, it supports various users to know all the objects which exist in the database and who can access it. One cannot remember all the tables, views constraints, etc in a huge database. If the user requires to explore one particular table.
  • When any DDL is called on the database objects, it examines the data dictionary for the object. Then underlying DBMS software transforms the object based on the DDL. These changes are displayed in the base tables and hence in the user views.
  • It controls access to different objects in the database by means of its views. It allows only the users who have proper rights to see the tables and views in the database. It masks other tables and views to which the user does not have access.
  • It provides a quick report on the data and the resources that the objects are using and hence making the data management easy.
  • Enforce the use of Data Standards.

If a data dictionary system is used only by the designers, users, and administrators and not by the DBMS Software, then it is called a passive data dictionary. Otherwise, it is described as an active data dictionary or data dictionary. When a passive data dictionary is modernized, it is done so manually and independently from any changes to a DBMS (database) structure. With an active data dictionary, the dictionary is refurbished first and changes transpire in the DBMS automatically as a result.

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