Back to the Top Recursive Relationships A Recursive Relationship is a relationship between an entity and itself. The E-R diagramming convention that shows a recursive relationship is known as a pig's ear. A hierarchy can be modeled as a recursive relationship. A recursive relationship MUST be optional in both directions. Use relationships to model roles.
Relationships allow a single entity instance to assume multiple roles.
Back to the Top Subtypes Power Point - Subtypes, Super types and Arcs Use subtypes to model exclusive entity types which have common attributes and common relationships. Supertype an entity that has subtypes. Subtype may not overlap. A Simple Entity is one which does not have any super or sub types. Back to the Top Exclusive Relationships Model two or more mutually exclusive relationships from the same entity using an arc.