7000 chapter 1.ppt

© 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 11

Chapter 3:Chapter 3:The Enhanced E-R ModelThe Enhanced E-R Model

Modern Database Modern Database ManagementManagement

1010thth Edition EditionJeffrey A. Hoffer, V. Ramesh, Jeffrey A. Hoffer, V. Ramesh,

Heikki TopiHeikki Topi

Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 22

ObjectivesObjectives Define termsDefine terms Understand use of supertype/subtype Understand use of supertype/subtype

relationshipsrelationships Understand use of specialization and Understand use of specialization and

generalization techniquesgeneralization techniques Specify completeness and disjointness constraintsSpecify completeness and disjointness constraints Develop supertype/subtype hierarchies for Develop supertype/subtype hierarchies for

realistic business situationsrealistic business situations Develop entity clustersDevelop entity clusters Explain universal (packaged) data modelExplain universal (packaged) data model Describe special features of data modeling Describe special features of data modeling

project using packaged data modelproject using packaged data model


Supertypes and SubtypesSupertypes and Subtypes Enhanced ER model: Enhanced ER model: extends original ER model extends original ER model

with new modeling constructswith new modeling constructs Subtype:Subtype: A subgrouping of the entities in an entity A 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 subgroupingssubgroupings

Supertype:Supertype: A generic entity type that has a A generic entity type that has a relationship with one or more subtypesrelationship with one or more subtypes

Attribute Inheritance:Attribute Inheritance: Subtype entities inherit values of all attributes of the Subtype entities inherit values of all attributes of the

supertypesupertype An instance of a subtype is also an instance of the An instance of a subtype is also an instance of the

supertypesupertype


Figure 3-1 Basic notation for supertype/subtype notation

a) EER notation


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

b) Microsoft

Visio Notation

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


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


Relationships and SubtypesRelationships and Subtypes

Relationships at the Relationships at the supertypesupertype level level indicate that all subtypes will indicate that all subtypes will participate in the relationshipparticipate in the relationship

The instances of a The instances of a subtypesubtype may may participate in a relationship unique to participate in a relationship unique to that subtype. In this situation, the that subtype. In this situation, the relationship is shown at the subtype relationship is shown at the subtype levellevel


Figure 3-3 Supertype/subtype relationships in a hospital

Both outpatients and resident patients are cared for by a responsible physician

Only resident patients are assigned to a bed


Generalization and Generalization and SpecializationSpecialization

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

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


Figure 3-4 Example of generalization

a) Three entity types: CAR, TRUCK, and MOTORCYCLE

All these types of vehicles have common attributes


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


Figure 3-5 Example of specialization

a) Entity type PART

Only applies to manufactured parts

Applies only to purchased parts


b) Specialization to MANUFACTURED PART and PURCHASED PART

Note: multivalued attribute was replaced by an associative entity relationship to another entity

Created 2 subtypes

Figure 3-5 Example of specialization (cont.)


Constraints in Supertype/ Constraints in Supertype/ Completeness ConstraintCompleteness Constraint

Completeness ConstraintsCompleteness Constraints: Whether : Whether an instance of a supertype an instance of a supertype mustmust also be a also be a member of at least one subtypemember of at least one subtype Total Specialization Rule: Yes (double line)Total Specialization Rule: Yes (double line) Partial Specialization Rule: No (single line)Partial Specialization Rule: No (single line)


Figure 3-6 Examples of completeness constraints

a) Total specialization rule


b) Partial specialization rule

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


Constraints in Supertype/ Constraints in Supertype/ Disjointness constraintDisjointness constraint

Disjointness ConstraintsDisjointness Constraints: : Whether an instance of a supertype may Whether an instance of a supertype may simultaneouslysimultaneously be a member of two (or be a member of two (or more) subtypesmore) subtypes Disjoint Rule: An instance of the supertype Disjoint Rule: An instance of the supertype

can be only ONE of the subtypescan be only ONE of the subtypes Overlap Rule: An instance of the supertype Overlap Rule: An instance of the supertype

could be more than one of the subtypescould be more than one of the subtypes


a) Disjoint rule

Figure 3-7 Examples of disjointness constraints


b) Overlap ruleFigure 3-7 Examples of disjointness constraints (cont.)


Constraints in Supertype/ Constraints in Supertype/ Subtype DiscriminatorsSubtype Discriminators

Subtype DiscriminatorSubtype Discriminator: An attribute : An attribute of the supertype whose values determine of the supertype whose values determine the target subtype(s)the target subtype(s) DisjointDisjoint – a – a simplesimple attribute with alternative attribute with alternative

values to indicate the possible subtypesvalues to indicate the possible subtypes OverlappingOverlapping – a – a compositecomposite attribute whose attribute whose

subparts pertain to different subtypes. Each subparts pertain to different subtypes. Each subpart contains a Boolean value to indicate subpart contains a Boolean value to indicate whether or not the instance belongs to the whether or not the instance belongs to the associated subtypeassociated subtype


Figure 3-8 Introducing a subtype discriminator (disjoint rule)


Figure 3-9 Subtype discriminator (overlap rule)


Figure 3-10 Example of supertype/subtype hierarchy


Entity ClustersEntity Clusters

EER diagrams are difficult to read when EER diagrams are difficult to read when there are too many entities and there are too many entities and relationshipsrelationships

Solution: Group entities and relationships Solution: Group entities and relationships into into entity clustersentity clusters

Entity clusterEntity cluster: Set of one or more entity : Set of one or more entity types and associated relationships types and associated relationships grouped into a single abstract entity typegrouped into a single abstract entity type


Figure 3-13a Possible entity clusters for Pine Valley Furniture in Microsoft Visio

Related groups of entities could become clusters


Figure 3-13b EER diagram of PVF entity clusters

More readable, isn’t it?


Figure 3-14 Manufacturing entity cluster

Detail for a single cluster


Packaged Data ModelsPackaged Data Models

Predefined data modelsPredefined data models Could be universal or industry-Could be universal or industry-

specificspecific Universal data model = a generic or Universal data model = a generic or

template data model that can be template data model that can be reused as a starting point for a data reused as a starting point for a data modeling project (also called a modeling project (also called a “pattern”)“pattern”)


Advantages of Packaged Data Advantages of Packaged Data ModelsModels

Use proven model componentsUse proven model components Save time and costSave time and cost Less likelihood of data model errorsLess likelihood of data model errors Easier to evolve and modify over timeEasier to evolve and modify over time Aid in requirements determinationAid in requirements determination Easier to readEasier to read Supertype/subtype hierarchies promote reuseSupertype/subtype hierarchies promote reuse Many-to-many relationships enhance model flexibilityMany-to-many relationships enhance model flexibility Vendor-supplied data model fosters integration with Vendor-supplied data model fosters integration with

vendor’s applicationsvendor’s applications Universal models support inter-organizational systemsUniversal models support inter-organizational systems


Packaged data models are generic models that can be customized for a particular organization’s business rules

Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model

(a) Basic PARTY universal data model


Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model

(b) PARTY supertype/subtype hierarchy


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