© 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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 33
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 44
Figure 3-1 Basic notation for supertype/subtype notation
a) EER notation
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 55
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.)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 66
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 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 77
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 88
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 99
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1010
Figure 3-4 Example of generalization
a) Three entity types: CAR, TRUCK, and MOTORCYCLE
All these types of vehicles have common attributes
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1111
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 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1212
Figure 3-5 Example of specialization
a) Entity type PART
Only applies to manufactured parts
Applies only to purchased parts
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1313
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.)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1414
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)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1515
Figure 3-6 Examples of completeness constraints
a) Total specialization rule
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1616
b) Partial specialization rule
Figure 3-6 Examples of completeness constraints (cont.)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1717
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1818
a) Disjoint rule
Figure 3-7 Examples of disjointness constraints
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 1919
b) Overlap ruleFigure 3-7 Examples of disjointness constraints (cont.)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2020
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2121
Figure 3-8 Introducing a subtype discriminator (disjoint rule)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2222
Figure 3-9 Subtype discriminator (overlap rule)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2323
Figure 3-10 Example of supertype/subtype hierarchy
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2424
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2525
Figure 3-13a Possible entity clusters for Pine Valley Furniture in Microsoft Visio
Related groups of entities could become clusters
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2626
Figure 3-13b EER diagram of PVF entity clusters
More readable, isn’t it?
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2727
Figure 3-14 Manufacturing entity cluster
Detail for a single cluster
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2828
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”)
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 2929
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 3030
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
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 3131
Figure 3-15 PARTY, PARTY ROLE, and ROLE TYPE in a universal data model
(b) PARTY supertype/subtype hierarchy
Chapter 3 © 2011 Pearson Education, Inc. Publishing as Prentice Hall© 2011 Pearson Education, Inc. Publishing as Prentice Hall 3232
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic,
mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Copyright © 2011 Pearson Education, Inc. Publishing as Prentice HallHall