Data dictionary

A data dictionary is a collection of database metadata, which is data about data. One kind of data dictionary is a human view of entities, attributes, and relationships, called a designer's data dictionary. There is usually a data dictionary that is internal to the DBMS, called a system catalog, which contains additional system-generated metadata. A designer's data dictionary can be derived from the system catalog, and the terms "data dictionary" and "system catalog" are often used interchangeably.

## Purpose[edit]

The purpose of a data dictionary is to make sure that all of the people who design and implement the database are on the same page in light of the entities, attributes, and relationships.

## Database Designer's Database[edit]

A data dictionary is sometimes called a database designer's database because it defines choices made in light of database design of entities and their characteristics.