the enhanced er model and business rules

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2007 by Prentice Hall 2007 by Prentice Hall 11

Chapter 4:Chapter 4:The Enhanced ER ModelThe Enhanced ER Model

and Business Rulesand Business Rules

Modern DatabaseModern Database

ManagementManagement

88thth

EditionEditionJefrey A. Hofer, Mary B. Prescott,Jefrey A. Hofer, Mary B. Prescott,

Fred R. McFaddenFred R. McFadden


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Chapter 4 2007 by Prentice Hall 2007 by Prentice Hall 22

ObjectivesObjectives

Defnition o termsDefnition o terms se o supert!pe"subt!pe relationshipsse o supert!pe"subt!pe relationships se o #enerali$ation and speciali$ationse o #enerali$ation and speciali$ation

techni%uestechni%ues &pecifcation o completeness and disjointness&pecifcation o completeness and disjointness

constraintsconstraints Develop supert!pe"subt!pe hierarchies orDevelop supert!pe"subt!pe hierarchies or

realistic business situationsrealistic business situations


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&upert!pes and &ubt!pes&upert!pes and &ubt!pes

&ubt!pe:&ubt!pe:' sub#roupin# o the entities in an' sub#roupin# o the entities in anentit! t!pe that has attributes distinct romentit! t!pe that has attributes distinct romthose in other sub#roupin#sthose in other sub#roupin#s

&upert!pe:&upert!pe:' #eneric entit! t!pe that has a' #eneric entit! t!pe that has arelationship (ith one or more subt!pesrelationship (ith one or more subt!pes

'ttribute )nheritance:'ttribute )nheritance: &ubt!pe entities inherit values o all&ubt!pe entities inherit values o all

attributes o the supert!peattributes o the supert!pe 'n instance o a subt!pe is also an instance'n instance o a subt!pe is also an instance

o the supert!peo the supert!pe


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*i#ure 4+, Basic notation or supert!pe"subt!pe notation

a- EER

notation


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Di.erent modelin# tools ma! have di.erent notation or thesame modelin# constructs

b-

Microsot/isio

0otation

*i#ure 4+, Basic notation or supert!pe"subt!pe notation 1cont2-


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Figure 4-2 Employee supertype it! t!ree subtypes

All employee subtypes

will have emp nbr, name,address, and date-hired

Each employee subtypewill also have its own

attributes


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Relationships and &ubt!pesRelationships and &ubt!pes

Relationships at theRelationships at the suertyesuertyelevellevel

indicate that all subt!pes (illindicate that all subt!pes (ill

participate in the relationshipparticipate in the relationshipThe instances o aThe instances o a subtyesubtyema!ma!

participate in a relationship uni%ue toparticipate in a relationship uni%ue to

that subt!pe2 )n this situation3 thethat subt!pe2 )n this situation3 therelationship is sho(n at the subt!perelationship is sho(n at the subt!pe

levellevel


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Chapter 4 2007 by Prentice Hall 2007 by Prentice Hall ""

Figure 4-3 #upertype$subtype relations!ips in a !ospital

Both

outpatients

and residentpatients are

cared for by

a responsible

physician

Only resident patients are

assigned to a bed


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Chapter 4 2007 by Prentice Hall 2007 by Prentice Hall %%

enerali$ation andenerali$ation and

&peciali$ation&peciali$ation !enera"i#ation$!enera"i#ation$The process oThe process o

defnin# a more #eneral entit! t!pe romdefnin# a more #eneral entit! t!pe rom

a set o more speciali$ed entit! t!pes2a set o more speciali$ed entit! t!pes2BOTTOM+5BOTTOM+5

%ecia"i#ation$%ecia"i#ation$The process oThe process o

defnin# one or more subt!pes o thedefnin# one or more subt!pes o thesupert!pe and ormin# supert!pe"subt!pesupert!pe and ormin# supert!pe"subt!pe

relationships2 TO5+DO60relationships2 TO5+DO60


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Figure 4-4 E&ample o' generali(ation

a) *!ree entity types+ ,./ *.,/ an *.,,E

All these types of vehicles have common attributes


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Figure 4-4 E&ample o' generali(ation cont8)

So we put

the sharedattributes in

a supertype

ote! no subtype for motorcycle, since it has no uni"ue

attributes

b) 9enerali(ation to :EH;,E supertype


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Figure 4-5 E&ample o' speciali(ation

a) Entity type P.*

Onl! applies tomanuactured parts

'pplies onl! to purchased part


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b) #peciali(ation to


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Constraints in &upert!pe"Constraints in &upert!pe"

Completeness ConstraintCompleteness Constraint &om"eteness &onstraints&om"eteness &onstraints: 6hether: 6hether

an instance o a supert!pean instance o a supert!pe mustmustalso be aalso be amember o at least one subt!pemember o at least one subt!peTotal &peciali$ation Rule: 7es 1double line-Total &peciali$ation Rule: 7es 1double line-

5artial &peciali$ation Rule: 0o 1sin#le line-5artial &peciali$ation Rule: 0o 1sin#le line-


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Figure 4-6 E&amples o' completeness constraints

a) *otal speciali(ation rule

A patient must be either

an outpatient or aresident patient


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b) Partial speciali(ation rule

A vehicle

could be a

car, a truc$,or neither

Figure 4-6 E&amples o' completeness constraints cont8)


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Disjointness constraintDisjointness constraint Dis'ointness &onstraintsDis'ointness &onstraints: 6hether: 6hether

an instance o a supert!pe ma!an instance o a supert!pe ma!

simultaneouslysimultaneouslybe a member o t(o 1orbe a member o t(o 1ormore- subt!pesmore- subt!pes Disjoint Rule: 'n instance o the supert!peDisjoint Rule: 'n instance o the supert!pe

can be onl! O0E o the subt!pescan be onl! O0E o the subt!pes

Overlap Rule: 'n instance o the supert!peOverlap Rule: 'n instance o the supert!pe

could be more than one o the subt!pescould be more than one o the subt!pes

'


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Chapter 4 2007 by Prentice Hall 2007 by Prentice Hall 1"1"

a) =is>oint rule

Figure 4-7 E&amples o' is>ointness constraints

A patient can either be outpatient

or resident, but not both


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Chapter 4 2007 by Prentice Hall 2007 by Prentice Hall 1%1%

b) ?erlap rule

A part may be bothpurchased and

manufactured

Figure 4-7 E&amples o' is>ointness constraints cont8)


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&ubt!pe Discriminators&ubt!pe Discriminators %ubtye Discriminator%ubtye Discriminator: 'n attribute: 'n attribute

o the supert!pe (hose values determineo the supert!pe (hose values determine

the tar#et subt!pe1s-the tar#et subt!pe1s- DisjointDisjoint8 a8 a simplesimpleattribute (ith alternativeattribute (ith alternative

values to indicate the possible subt!pesvalues to indicate the possible subt!pes

OverlappingOverlapping8 a8 a compositecompositeattribute (hoseattribute (hose

subparts pertain to di.erent subt!pes2 Eachsubparts pertain to di.erent subt!pes2 Eachsubpart contains a boolean value to indicatesubpart contains a boolean value to indicate

(hether or not the instance belon#s to the(hether or not the instance belon#s to the

associated subt!peassociated subt!pe

di j i t


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Figure 4-" ;ntroucing a subtype iscriminator disjointrule)

A simple attribute with

different possible values

indicating the subtype


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Figure 4-% #ubtype iscriminator overlaprule)A composite

attribute with

sub-attributes

indicating %yes&or %no& to

determine

whether it is of

each subtype


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Figure 4-10 E&ample o' supertype$subtype !ierarc!y

the enhanced er model and business rules

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