Semantics of recursive relationships in entity-relationship model
The recursive relationship of the ER model is used to represent a hierarchical situation in a natural way. However, the semantics of recursive relationships are quite difficult to grasp because entities carry out different roles in relationships. This article proposes four classes of entity types allowed in recursive relationships and provides a thorough analysis of all the types of recursive relationships through the four types of the recursive dependency and four classes of the entity type. By the proposed concepts of the entity type properties and the existing relationship constraints of the recursive relationships, we can more clearly capture the semantics of hierarchical structures and integrity constraints in practical databases.
recursive relationship entity-relationship model recursive dependency