1. Enhanced ER modeling techniques Transparencies
Chapter 11
Enhanced ER modeling techniques
Transparencies
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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.
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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.
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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.
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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.
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The EER model
One of the most useful concepts associated with the EER model is called specialization/generalization.
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7. Specialization/generalization
Associated with special types of entities known as superclasses and subclasses, and the process of attribute inheritance.
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8. Superclasses and subclasses
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.
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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.
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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.
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11. AllStaff table holding details of all staff
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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.
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13. Specialization/generalization
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.
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14. Staff entity with subclasses representing job roles
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15. Shared subclass and a subclass with its own subclass
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16. 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.
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17. Vehicle entity into vehicle types
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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
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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
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20. Creating tables to represent specialization/generalization
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21. Tables representing Staff and the Branch entities
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22. Tables representing the Vehicle entity
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