Enhanced Entity Relationship Modeling - Database Design - Lecture Slides, Slides of Database Management Systems (DBMS)

Download Enhanced Entity Relationship Modeling - Database Design - Lecture Slides and more Slides Database Management Systems (DBMS) in PDF only on Docsity!

Enhanced Entity Relationship Modeling

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

• 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

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

4 Possibilities {Mandatory, And} {Mandatory, Or} {Optional, And} {Optional, Or} Docsity.com

• 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”

• 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