GCSE Link: 7.07 (Relational Databases)

An entity is a distinct category of object, person, item or concept about which data is to be recorded in a database.

It is essentially a single table which contains information about a thing. For example, in the context of a library's database, possible entities (tables) are Book, Member, and Computer.

An attribute is a single property of a given entity.

The attributes of an entity are the field names for the table of that entity. For example, for the Book entity, possible attributes include BookID, Title, DateLoaned, DateDue, and MemberID.

An entity can be described in terms of its attributes. For example, you could write Book(BookID, Title, DateLoaned, DateDue, MemberID). Note that BookID is underlined because it is the entity identifier (primary key of the corresponding table). However, we now learn at A Level that the entity identifier can be a combination of multiple attributes which can uniquely identify each record. In this case, it is called a composite identifier.

Entity relationship (ER) diagrams can be drawn to demonstrate if relationships are one-to-one, one-to-many, or many-to-many.

Diagram 1 shows an example ER diagram.

Diagram 1

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Define the term "foreign key".

A foreign key is a field/attribute which is the primary key/entity identifier of another table/entity.

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