Chapter 4 - 2-10 - CGS 2545: Database Concepts Spring 2010...

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CGS 2545: Database Concepts (Chapter 4) Page 1 © Mark Llewellyn CGS 2545: Database Concepts Spring 2010 Chapter 4 – The Enhanced ER Model And Business Rules School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn [email protected] HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cgs2545/spr2010
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CGS 2545: Database Concepts (Chapter 4) Page 2 © Mark Llewellyn Chapter 4 Objectives Definition of terms. Use of supertype/subtype relationships. Use of generalization and specialization techniques. Specification of completeness and disjointness constraints. Develop supertype/subtype hierarchies for common business situations. Develop entity clusters. Name categories of business rules. Define operational constraints graphically and in English.
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CGS 2545: Database Concepts (Chapter 4) Page 3 © Mark Llewellyn Introduction The basic ER model was introduce in the 1970s. It has been widely accepted as a suitable model for most business situations. However, the business environment has changed substantially in the 30 plus years that have elapsed since the introduction of the model. Business relationships are now more complex, and as a result, business data is much more complex. To cope with these changes the ER model has been enhanced in many areas since it was first introduced so that it can more accurately represent the complex data encountered in today’s business environment. The term enhanced entity-relationship (EER) model is used to identify the model that has results from extending the original ER model with new modeling constructs. Two main extensions to the ER model incorporated in the EER model are: (1) supertype/subtype relationships , and (2) entity clustering techniques .
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CGS 2545: Database Concepts (Chapter 4) Page 4 © Mark Llewellyn Supertypes and Subtypes Subtype: A subgrouping of the entities in an entity type which has attributes that are distinct from those in other subgroupings. Supertype: An generic entity type that has a relationship with one or more subtypes. Attribute Inheritance: Subtype entities inherit values of all attributes of the supertype. An instance of a subtype is also an instance of the supertype.
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CGS 2545: Database Concepts (Chapter 4) Page 5 © Mark Llewellyn
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CGS 2545: Database Concepts (Chapter 4) Page 6 © Mark Llewellyn Relationships and Subtypes Relationships at the supertype level indicate that all subtypes will participate in the relationship. The instances of a subtype may participate in a relationship unique to that subtype. In this situation, the relationship is shown at the subtype level.
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CGS 2545: Database Concepts (Chapter 4) Page 7 © Mark Llewellyn
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CGS 2545: Database Concepts (Chapter 4) Page 8 © Mark Llewellyn When To Use Supertype/Subtype Relationships Whether to use supertype/subtype relationships is a decision the data modeler must make in each situation. You should consider using subtypes when either (or
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This note was uploaded on 10/05/2010 for the course CGS 2545C CGS 2545c taught by Professor L during the Spring '10 term at University of Central Florida.

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Chapter 4 - 2-10 - CGS 2545: Database Concepts Spring 2010...

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