Analyzing Data › Data Modeling Terminology › Entity Subtype and Partitioning

Entity Subtype and Partitioning

You find that entities of a single entity type have different or more attributes and relationships. This situation requires the definition of entity subtypes and partitioning.

An entity subtype is a description of entities of the same type that is more restrictive than that of the entity type and to which more common relationships and attributes apply.

Partitioning is a basis for subdividing the entities of one type into subtypes.

For example, the following table shows the partitioning of the entity type CUSTOMER.

Although all CUSTOMERs share a set of relationships and attributes, some CUSTOMERs (FOREIGN ones) have relationships and attributes beyond those in the common set, and others (DOMESTIC ones) have different relationships and attributes in addition to the common set. This can be seen as specializing the set of CUSTOMER entities for a specific purpose. The entities are partitioned in this example based on the nationality of a customer.

It is possible to partition customer entities in many ways, for example, whether the customer is external to the enterprise or some other division internal to the corporation.

You can define these mutually exclusive groups of entities of the same type as entity subtypes belonging to a partitioning.