1. Chapter 3: The Enhanced E-R Model
Modern Database Management
11th Edition, International Edition
Jeffrey A. Hoffer, V. Ramesh,
Heikki Topi
© 2013 Pearson Education

2. Objectives Define terms
Understand the use of supertype/subtype relationships
Understand the 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

3. Supertype/Subtype Relationships
Enable us to model a general entity type (called supertype) and then subdivide it into several specialized entity types (called subtypes)
A new modeling construct for extending the original ER model. The extended result model is the Enhanced (加 強的) ER Model
Example 1:
Supertype : Car
Subtypes : sedan, sports car, coupe, and so on.
Example 2:
Supertype : Vechicle
Subtypes : Car, Motorcycle, Bike, Ship, and so on.

4. Supertypes and Subtypes
A subgrouping of the entities in an entity type that has attributes distinct from those in other subgroupings
Supertype (超類別、父類別)
A generic entity type that has a relationship with one or more subtypes
Example
Supertype : Student
Subtypes : Undergraduate student, Graduate students
Attribute Inheritance
An instance of a subtype is also an instance of the supertype
A subtype entity inherit all attributes of the supertype

5. Figure 3-1 Basic notation for supertype/subtype notation
a) EER notation
(通用化的)
(特化的)
© 2013 Pearson Education
Chapter 3 5

6. Figure 3-1 Basic notation for supertype/subtype notation (cont.)
b) Microsoft Visio Notation
Different modeling tools may have different notation for the same modeling constructs.
© 2013 Pearson Education
Chapter 3 6

7. Data Modeling with many subtypes
Case : An organization with three basic types of employees
Hourly employees
Salaried employees
Contract employees
Choices for developing a conceptual data model
Define a single entity type
Advantage : simple
Disadvantage : an entity instance contain all the attributes for the three types of employees. Some of the attributes are null.
Define a separate entity type for each of the entities
Disadvantage : fails to exploit common properties of employees.
Define a supertype with three subtypes
Attributes of three basic types

8. Figure 3-2 Employee supertype with three subtypes
(An example of data model with many subtypes)
All EMPLOYEE subtypes will have employee number, name, address, and date hired
Each EMPLOYEE subtype will also have its own attributes
© 2013 Pearson Education
Chapter 3 8

9. Relationships and Subtypes
Relationship at the supertype level
indicate that all subtypes will participate in the relationship
Relationship at the subtype level
The instances of a subtype may participate in a relationship unique to that subtype.

10. Figure 3-3 Supertype/subtype relationships in a hospital
relationship at supertype level
relationship at subtype level
(門診病患，院外病患)
© 2013 Pearson Education
Chapter 3 10

11. Generalization and Specialization
The process of defining a more general entity type from a set of more specialized entity types.
(BOTTOM-UP process for creating a supertype/subtype relationship)
The common attributes are put in the supertype.
Specialization (特用化)
The process of defining one or more subtypes from the supertype and forming supertype/subtype relationship.
(TOP-DOWN process for creating a supertype/subtype relationship)
Each subtype is formed with some distinguished attributes.

12. Figure 3-4 Example of generalization process
a) Three entity types: CAR, TRUCK, and MOTORCYCLE
What are the common attributes for all these types of vehicles ?
What is the supertype/subtype relationship ?
© 2013 Pearson Education
Chapter 3 12

13. Figure 3-4 Example of generalization process
b) Generalization to VEHICLE supertype
So we put the shared attributes in a supertype
Note
No subtype for motorcycle, since it has no unique attributes
The only attributes of MOTOTCYCLE are those common to all vehicles
© 2013 Pearson Education
Chapter 3 13

14. Figure 3-5 Example of specialization process
a) Entity type PART
Only applies to manufactured parts
Applies only to purchased parts
(a multivalued composite attribute)
What are the attributes specific to each of subtypes?
What is the supertype/subtype relationship ?
© 2013 Pearson Education
Chapter 3 14

15. Figure 3-5 Example of specialization process
b) Specialization to MANUFACTURED PART and PURCHASED PART
Created 2 subtypes
Note : the multivalued composite attribute was replaced by an associative entity relationship to another entity
© 2013 Pearson Education
Chapter 3 15

16. Constraints in Supertype/SUBTYPE RELATIONSHIPS
Completeness Constraints (完全性限制)
Whether an instance of a supertype must also be a member of at least one subtype
Total Specialization Rule: Yes (double line)
Each entity instance of the supertype must be a member of some subtype in the relationship.
Partial Specialization Rule: No (single line)
An entity instance of the supertype is allowed not to belong to any subtype.

17. Figure 3-6 Examples of completeness constraints
a) Total specialization rule
© 2013 Pearson Education
Chapter 3 17

18. Figure 3-6 Examples of completeness constraints (cont.)
b) Partial specialization rule
A vehicle can be a motorcycle
© 2013 Pearson Education
Chapter 3 18

19. Constraints in Supertype/SUBTYPE RELATIONSHIPS
Disjointness Constraints (無重疊性限制)
Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes
Disjoint Rule:
An instance of the supertype can be only a member of ONE of the subtypes
Overlap Rule:
An instance of the supertype could be a member of more than one of the subtypes
© 2013 Pearson Education
Chapter 3 19

20. Figure 3-7 Examples of disjointness constraints
a) Disjoint rule
PATIENT
OUTPATIENT
RESIDENCE
© 2013 Pearson Education
Chapter 3 20

21. When does this situation happen ?
Figure 3-7 Examples of disjointness constraints (cont.)
b) Overlap rule
PART
M PART
P PART
PART
M PART
P PART
When does this situation happen ?
© 2013 Pearson Education
Chapter 3 21

22. Constraints in Supertype/SUBTYPE RELATIONSHIPS
Subtype Discriminator (區別屬性)
An attribute of the supertype whose values determine the target subtype(s)
For disjoint subtypes
a simple attribute with different values to indicate the possible subtypes
For overlapping subtypes
a composite attribute whose subparts pertain to different subtypes. Each subpart contains a Boolean value to indicate whether or not the instance belongs to the associated subtype
© 2013 Pearson Education
Chapter 3 22

23. Figure 3-8 Introducing a subtype discriminator (disjoint rule)
© 2013 Pearson Education
Chapter 3 23

24. Figure 3-9 Subtype discriminator (overlap rule)
1. Three cases:
Y, Y
Y, N
N, Y
2. Why 3 cases?
© 2013 Pearson Education
Chapter 3 24

25. Figure 3-10 Example of supertype/subtype hierarchy
Case 3
Case 2
Case 1
What is the situation for each case?
completeness constraint
disjointness constraint
subtype discriminator design
© 2013 Pearson Education
Chapter 3 25

26. Entity Clusters
EER diagrams are difficult to read when there are too many entities and relationships.
Solution:
Group entities and relationships into entity clusters.
Entity cluster
A set of one or more entity types and associated relationships grouped into a single abstract (virtual) entity type

27. Figure 3-13a Possible entity clusters for Pine Valley Furniture in Microsoft Visio
Related groups of entities could become entity clusters

28. Figure 3-13b EER diagram of entity clusters for Pine Valley Furniture
More readable, isn’t it?
© 2013 Pearson Education
Chapter 3 28

29. Figure 3-14 Manufacturing entity cluster
Detail for a single cluster
© 2013 Pearson Education
Chapter 3 29

30. Packaged Data Models Predefined data models
Can be customized for a particular organization’s business rules
Could be universal or industry-specific
Universal (通用的) data model
(also called a “pattern”)
A generic or template data model that can be reused as a starting point for a data modeling project

31. Advantages of Packaged Data Models
Use proven model components
Save time and cost
Less likelihood of data model errors
Easier to evolve and modify over time
Aid in requirements determination
Easier to read
Supertype/subtype hierarchies promote reuse
Many-to-many relationships enhance model flexibility
Vendor-supplied data model fosters integration with vendor’s applications
Universal models support inter-organizational systems

32. Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model
PARTY (参與方) generalize persons or organizations as actors for the enterprise
ROLE TYPE
allows a specific party to serve in different roles during different time periods.
PARTY ROLE generalizes various roles parties can play at different times
A PARTY ROLE instance is a situation in which a PARTY acts in a particular ROLE TYPE.
(a) Basic PARTY universal data model
© 2013 Pearson Education
Chapter 3 32

33. Figure 3-15 (b) PARTY supertype/subtype hierarchy
One PARTY supertype with many subtypes covering many party roles
© 2013 Pearson Education
Chapter 3 33

34. 作業 下一週第一堂上課時交 作業#1 第三章 Problems and Exercises (177~180頁) 學號單號:
3 : a, c
8 : a, c 14
學號雙號:
3 : b, d
8 : b, d

35. Copyright © 2013 Pearson Education35