Chapter 13 - Enhanced Entity-Relationship Modeling

Composition

A specific form of aggregation that represents an association between entities, where there is a strong ownership and coincidental lifetime between the "whole" and the "part."

shared subclass

A subclass with more than one superclass Results in multiple inheritance

Superclass

An entity type that includes one or more distinct subgroupings of its occurrences, which must be represented in a data model.

Subclass

A distinct subgrouping of occurrences of an entity type, which must be represented in a data model. Every sub a member of super...but not all super members of subs.

Disjoint constraint

Describes the relationship between members of the subclasses and indicates whether it is possible for a member of a superclass to be a member of one, or more than one, subclass (The disjoint constraint only applies when a superclass has more than one subclass. If the subclasses are disjoint, then an entity occurrence can be a member of only one of the subclasses.)

Participation constraint

Determines whether every member in the superclass must participate as a member of a subclass. Mandatory or Optional

ER vs EER

ER (entity relationship) includes: - entities - relationships - attributes EER (enhanced entity relationship) also includes: - specialization/generalization (superclass/subclass) - aggregation ("has-a" or "is-part-of" relationship) - composition (association between entities, "whole" and the "part.")

EER is used for

Enhanced Entity Relationship Model CAD CAM (computer aided manufacturing) CASE (computer aided software engineering) OIS (office information systems) EER byproduct of a need for "semantic" modeling concepts

The process of minimizing the differences between entities by identifying their common characteristics.

Generalization - top-down

Aggregation

Represents a "has-a" or "is-part-of" relationship between entity types, where one represents the "whole" and the other the "part."

The process of maximizing the differences between members of an entity by identifying their distinguishing characteristics.

Specialization - bottom-up