Pearson Education Limited, 20042 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 EntityRelationship (EER) model called specialization/generalization.
Pearson Education Limited, 20043 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, 20044 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, 20045 The EER model Stimulated need to develop additional semantic modeling concepts. Original ER model with additional semantic concepts is referred to as the Enhanced EntityRelationship (EER) model.
Pearson Education Limited, 20046 The EER model One of the most useful concepts associated with the EER model is called specialization/generalization.
Pearson Education Limited, 20047 Specialization/generalization Associated with special types of entities known as superclasses and subclasses, and the process of attribute inheritance.
Pearson Education Limited, 20048 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, 20049 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, 200410 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, 200411 AllStaff table holding details of all staff
Pearson Education Limited, 200412 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, 200413 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, 200415 Shared subclass and a subclass with its own subclass
Pearson Education Limited, 200416 Constraints on specialization/ generalization Two constraints may apply to a specialization/generalization called participation constraints and disjoint constraints. Participation constraint Determines whether every occurrence in the superclass must participate as a member of a subclass. May be mandatory or optional.
Pearson Education Limited, 200417 Vehicle entity into vehicle types
Pearson Education Limited, 200418 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, 200419 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, 200420 Creating tables to represent specialization/generalization
Pearson Education Limited, 200421 Tables representing Staff and the Branch entities
Pearson Education Limited, 200422 Tables representing the Vehicle entity
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