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Chapter 11

Chapter 11. Enhanced ER modeling techniques Transparencies. Chapter 11 - Objectives. The limitations of the basic ER modeling concepts and the requirements to model more complex applications using enhanced data modeling concepts.

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Chapter 11

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  1. Chapter 11 Enhanced ER modeling techniques Transparencies © Pearson Education Limited, 2004

  2. Chapter 11 - Objectives • The limitations of the basic ER modeling concepts and the requirements to model more complex applications using enhanced data modeling concepts. • The main concepts associated with the Enhanced Entity–Relationship (EER) model called specialization/generalization. © Pearson Education Limited, 2004

  3. Chapter 11 - Objectives • A notation for displaying specialization/generalization in an EER diagram. • How to create tables that represent specialization/generalization in an EER model. © Pearson Education Limited, 2004

  4. The EER model • Basic concepts are often perfectly adequate for the representation of the data requirements for many different database applications. • However, basic concepts can be limiting when modeling more complex database applications with a large amount of data and/or data with complex interrelationships. © Pearson Education Limited, 2004

  5. The EER model • Stimulated need to develop additional ‘semantic’ modeling concepts. • Original ER model with additional semantic concepts is referred to as the Enhanced Entity–Relationship (EER) model. © Pearson Education Limited, 2004

  6. The EER model • One of the most useful concepts associated with the EER model is called specialization/generalization. © Pearson Education Limited, 2004

  7. Specialization/generalization • Associated with special types of entities known as superclasses and subclasses, and the process of attribute inheritance. © Pearson Education Limited, 2004

  8. Superclasses and subclasses • Superclass • An entity that includes one or more distinct groupings of its occurrences, which require to be represented in a data model. • Subclass • A distinct grouping of occurrences of an entity type, which require to be represented in a data model. © Pearson Education Limited, 2004

  9. Superclass/subclass relationship • Superclass/subclass relationship is one-to-one (1:1). • Each member of a subclass is also a member of the superclass but has a distinct role. © Pearson Education Limited, 2004

  10. Superclasses and subclasses • We can use superclasses and subclasses to avoid describing different types of entities with possibly different attributes within a single entity. • Can also show relationships that are only associated with particular subclasses and not with superclass. © Pearson Education Limited, 2004

  11. AllStaff table holding details of all staff © Pearson Education Limited, 2004

  12. Attribute inheritance • An entity occurrence in a subclass represents the same ‘real world’ object as in the superclass. • Hence, a member of a subclass inherits those attributes associated with the superclass, but may also have subclass-specific attributes. © Pearson Education Limited, 2004

  13. Specialization/generalization • Specialization • The process of maximizing the differences between members of an entity by identifying their distinguishing characteristics. • Generalization • The process of minimizing the differences between entities by identifying their common characteristics. © Pearson Education Limited, 2004

  14. Staff entity with subclasses representing job roles © Pearson Education Limited, 2004

  15. Shared subclass and a subclass with its own subclass © Pearson Education Limited, 2004

  16. Constraints on specialization/ generalization • Two constraints may apply to a specialization/generalization called participation constraints and disjoint constraints. • Participationconstraint • Determines whether every occurrence in the superclass must participate as a member of a subclass. • May be mandatory or optional. © Pearson Education Limited, 2004

  17. Vehicle entity into vehicle types © Pearson Education Limited, 2004

  18. Constraints on specialization / generalization • 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. • May be disjoint or nondisjoint © Pearson Education Limited, 2004

  19. Constraints on specialization / generalization • There are four categories of constraints of specialization and generalization: • mandatory and disjoint • optional and disjoint • mandatory and nondisjoint • optional and nondisjoint © Pearson Education Limited, 2004

  20. Creating tables to represent specialization/generalization © Pearson Education Limited, 2004

  21. Tables representing Staff and the Branch entities © Pearson Education Limited, 2004

  22. Tables representing the Vehicle entity © Pearson Education Limited, 2004

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