MIS 325 Lecture Notes - Lecture 6: Subtyping, Abstract And Concrete, Unique Key

• School: UT-Austin
• Department: Management Information Systems
• Course: MIS 325
• Professor: John Mote

Document Summary

Advanced data modeling completeness constraint - a constraint that specifies whether each entity supertype occurrence must also be a member of at least one subtype. The completeness constraint can be partial or total. Partial completeness means that some supertype occurrences might not be members of any subtype. The most common design trap is known as a fan trap. disjoint subtype (nonoverlapping subtype) - in a specialization hierarchy, a unique and nonoverlapping subtype entity set. An entity cluster is formed by combining multiple interrelated entities into a single abstract entity object. An entity cluster is considered virtual or abstract because it is not actually an entity in the final erd. entity subtype - in a generalization/specialization hierarchy, a subset of an entity supertype. Specialization is based on grouping unique characteristics and relationships of the subtypes. subtype (entity set) - an entity that contains unique characteristics within a more broadly defined entity known as a supertype.