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Entity, Entity Types and Entity Sets

An entity is any object or thing in the real world that can be distinctly identified and represented in a database.

  • An entity can be a person, object, event, or concept that must have an attribute and a unique key.

    Example: In a university database, a “Student” or “Course” would be an entity.

    An entity type defines a collection of similar entities that share the same set of attributes.

    • It acts as a blueprint for describing entities of a particular kind in the database.

      Example: In a university database, the entity type “Student” may have attributes such as “Student ID,” “Name,” “Date of Birth,” and “Major.”

      An entity set is the collection of all entities of a particular entity type in a database at a given point in time.

      • It represents the complete set of instances of that entity type.

        Example: The entity set “Students” would contain all the students (entities) currently recorded in the university database.

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