Basic ER modeling was adequate for simpler databases, but in the 1980’s more demanding databases required more extensive modeling requirements. Some such applications:  CAD - Computer Aided Design  CAM – Computer Aided Manufacturing  CASE – Computer Assisted Software Engineering  OIS – Office Information Systems  GIS – Geographical Information Systems

EER adds 3 main additional semantic concepts for visual modeling of databases using UML(Unified Modeling Language). 1. Specialization/Generalization 1. Superclass 2. Subclass 3. Inheritance 2. Aggregation 3. Composition

 Very similar to Object Oriented programming superclass, subclass and inheritance.  Superclass: An entity type that includes one ore more subgroupings of its occurrences, which require to be represented in a data model.  Subclass: A distinct subgrouping of occurrences of an entity type, which require to be represented in a data model.  Superclass/Subclass relation is a 1:1 relation  Superclass may contain overlapping subclasses  Helps avoid multiple copies of the same data and null entries

 Subclasses inherit Superclasses attributes  Subclass is its own entity  Subclass may have its own subclasses  Shared Subclass: Entity with more than 1 Superclass : (Multiple Inheritance)  An entity and its Sublasses are called:  Type Hierarchy  Specialization Hierarchy  Generalization Hierarchy  Is-A Hierarchy

 Specialization: The process of maximizing the differences between members of an entity by identifying their distinguishing characteristics.  Specialization is a Top-Down approach  Generalization: The process of minimizing the differences between entities by identifying their common characteristics.  Generalization is a Bottom-Up approach

 Use an open triangle on the Superclass side to denote a SuperClass/Subclass relation.

 Participation Constraint: Determines whether every member of a superclass must participate as a member of a subclass.  Mandatory  Optional  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 subclasses.  Disjoint: Or  Nondisjoint: And

4 Possibilities {Mandatory, And} {Mandatory, Or} {Optional, And} {Optional, Or}

 Aggregation: Represents a “has-a” or “is-part- of” relationship between two entities.  Entirely conceptual, only distinguishing the “whole” from the “part”  Does not change the diagrammatic meaning or traversal of the relationship  Does not link the lifetimes of the “whole” and “part”

 Use an Open diamond on the “whole” side

 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 “part”.  In a Composite relationship the “whole” is responsible for the disposition of the relationship.  The “whole” is responsible for the creation and destruction of its parts.  An object may be part of only one composite at a time.

 Use a filled diamond on the “whole” side

By: Bryan Hunwardsen