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2. The Entity-Relationship Model of a Da... > 2.2. Entities and Their Attributes

Entities and Their Attributes

The purpose of a database is to store information about certain types of objects. In database language, these objects are called entities . For example, the entities of the LIBRARY database include books, authors, and publishers.

It is very important at the outset to make a distinction between the entities that are contained in a database at a given time and the world of all possible entities that the database might contain. The reason this is important is that the contents of a database are constantly changing and we must make decisions based not just on what is contained in a database at a given time, but on what might be contained in the database in the future.


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