CHAPTER 3:
CHAPTER 3:
THE ENHANCED E-R MODEL
THE ENHANCED E-R MODEL
© 2013 Pearson Education, Inc. #Publishing as Prentice Hall 1
Modern Database Management
11th Edition
Jeffrey A. Hoffer, V. Ramesh,
Heikki Topi
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CHAPTER 3:CHAPTER 3:
THE ENHANCED E-R MODEL THE ENHANCED E-R MODEL
© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Modern Database Management
th
Edition
Jeffrey A. Hoffer, V. Ramesh, Heikki Topi
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
OBJECTIVES OBJECTIVES
(^) Define termsDefine terms Understand use of supertype/subtype relationshipsUnderstand use of supertype/subtype relationships Understand use of specialization andUnderstand use of specialization and generalization techniques generalization techniques Specify completeness and disjointness constraintsSpecify completeness and disjointness constraints (^) Develop supertype/subtype hierarchies for realisticDevelop supertype/subtype hierarchies for realistic business situations business situations Develop entity clustersDevelop entity clusters (^) Explain universal (packaged) data modelExplain universal (packaged) data model Describe special features of data modeling projectDescribe special features of data modeling project using packaged data model using packaged data model
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
SUPERTYPES AND SUBTYPES SUPERTYPES AND SUBTYPES
Enhanced ER model:Enhanced ER model: extends original ER modelextends original ER model
with new modeling constructs with new modeling constructs
Subtype:Subtype: A subgrouping of the entities in an entityA subgrouping of the entities in an entity
type that has attributes distinct from those in other type that has attributes distinct from those in other subgroupings subgroupings
Supertype:Supertype: A generic entity type that has aA generic entity type that has a
relationship with one or more subtypes relationship with one or more subtypes
Attribute Inheritance:Attribute Inheritance:
(^) Subtype entities inherit values of all attributes of theSubtype entities inherit values of all attributes of the supertype supertype (^) An instance of a subtype is also an instance of theAn instance of a subtype is also an instance of the supertype supertype
Figure 3-1 Basic notation for supertype/subtype notation a) EER notatio n Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Figure 3-2 Employee supertype with three subtypes All employee subtypes will have employee number, name, address, and date hired Each employee subtype will also have its own attributes Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
RELATIONSHIPS AND SUBTYPES RELATIONSHIPS AND SUBTYPES
Relationships at theRelationships at the supertypesupertype levellevel
indicate that all subtypes will indicate that all subtypes will
participate in the relationship participate in the relationship
The instances of aThe instances of a subtypesubtype maymay
participate in a relationship unique to participate in a relationship unique to
that subtype. that subtype. In this situation, theIn this situation, the
relationship is shown at the subtype relationship is shown at the subtype
level level
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
The property by which subtype entities
inherit values of all attributes of the
supertype.
This important property makes it
unnecessary to include supertype
attributes redundantly with the
subtypes.
Figure 3-3 Supertype/subtype relationships in a hospital Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Figure 3-4 Example of generalization a) Three entity types: CAR, TRUCK, and MOTORCYCLE All these types of vehicles have common attributes Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Figure 3-4 Example of generalization (cont.) So we put the shared attributes in a supertype Note: no subtype for motorcycle, since it has no unique attributes b) Generalization to VEHICLE supertype Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
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© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Completeness Constraints: Whether an
instance of a supertype must also be a
member of at least one subtype
(^) Total Specialization Rule: Yes (double line) (^) Partial Specialization Rule: No (single line)
b) Partial specialization rule Figure 3-6 Examples of completeness constraints (cont.) Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall
Disjointness Constraints: 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 ONE of the subtypes (^) Overlap Rule: An instance of the supertype could be more than one of the subtypes Chapter 3 © 2013 Pearson Education, Inc. Publishing as Prentice Hall© 2013 Pearson Education, Inc. Publishing as Prentice Hall