Analyzing Data › Data Modeling Terminology › Entity and Entity Type

Entity and Entity Type

An entity is a fundamental thing of relevance to the enterprise about which data is kept. An entity is an occurrence of an entity type.

An entity type is a description of all the entities to which a common definition and common relationships and attributes apply. An entity type describes a collection of entities.

For example, consider a company that sells two kinds of products: ball bearings and steel tubes. Three customers buy these products. In this example, CUSTOMER and PRODUCT are both entity types, while the specific instances of CUSTOMER and PRODUCT are entities.

This following table shows the entity types and entities for this example:

For some entities, there are many individual occurrences physically present at one time. For example, there are many Ball bearings in inventory. For some of these entities, the business distinguish between individual occurrences and trace each of these occurrences. For example, steel tubes are installed in a nuclear reactor and distinguished with a serial number or some other identifying mark. Since this requires more information, steel tubes with serial numbers are seen as occurrences of the entity type NUMBERED PRODUCT.