Entity, Entity set and Attributes

An entity is a thing or object in the real world that is distinguishable from other objects. An entity can be concrete, such as a book or a person or it may be an abstract, such as a loan, holiday or a concept. An entity in a database system actually represents a table.

The properties or parts of an entity are called attributes. For example, a person has the attributes person_id, name, occupation, salary etc. A book has the attributes book_id, author, publisher, category, number of copies etc. Attributes are actually the fields of a database table or entity.

An entity set is a set of entities of the same type that share the same properties or attributes. For example, the set of all students who take a class can represent a student entity set in which each entity is a student sharing similar attributes with other students such as student_id, name, contact_no, address etc.

Copyright @ by Rosina S Khan