8.1.1: Entity Types

Each entity type is implemented with a separate relation. Entity types are either strong entity types or weak entity types.

• Strong Entities
  • Strong, or regular, entity types are mapped to their own relation. The PK is chosen from the set of keys available.

• Weak Entities
  • Weak entity types are mapped to their own relation, but the primary key of the relation is formed as follows. If there are any identifying relationships, then the PK of the weak entity is the combination of the PKs of entities related through identifying relationships and the discriminator of the weak entity type; otherwise, the PK of the relation is the PK of the weak entity.