Packaged data models

• Week 4

• Enhanced E-R diagram • Chapter 3

It is essential you read the book. These slides represent a summary of what was presented in the class and summary of what is covered in the book.

Relying purely on the slides will not guarantee you will pass this course.

Lesson Content

• Understand use of supertype/subtype relationships

• Understand use of specialization and generalization techniques

• Specify completeness and disjointness constraints

• Develop supertype/subtype hierarchies for realistic business situations

• Develop entity clusters

• Explain universal (packaged) data model

• Describe special features of data modeling project using packaged data model

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Supertypes and Subtypes

• Enhanced ER model: extends original ER model with new modeling constructs

• Subtype: A subgrouping of the entities in an entity type that has attributes distinct from those in other subgroupings

• Supertype: A 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 3

Different modeling tools may have different notation for the same modeling constructs.

Figure 3-1 Basic notation for supertype/subtype notation (cont.)

4

Generalization and Specialization

•Generalization: The process of defining a more general entity type from a set of more specialized entity types. BOTTOM-UP

•Specialization: The process of defining one or more subtypes of the supertype and forming supertype/subtype relationships. TOP-DOWN

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b) Specialization to MANUFACTURED PART and PURCHASED PART

Note: multivalued composite attribute was replaced by an associative

entity relationship to another entity

Created 2

subtypes

Figure 3-5 Example of specialization (cont.)

Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall

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b) Partial specialization rule

Figure 3-6 Examples of completeness constraints (cont.)

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a) Disjoint rule

Figure 3-7 Examples of disjointness constraints

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b) Overlap rule

Figure 3-7 Examples of disjointness constraints (cont.