The Extended Entity-Relationship Entities, Relationships, and Attributes An EER database contains data about entities and their relationships . Entities and relationships are qualified by attributes representing their descriptive properties. Similar entities, that is entities of the same type, are classified in entity-sets.
Attributes take their values from underlying primitive domains called value-sets .
Association-cardinalities can be either one or many . The involvement of objects in relationships is by default optional . The inverse of generalization is called specialization .