chapter 3 erd

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Chapter 3

Data Modeling Using theEntity-Relationship (ER) Model

Copyright © 2004 Pearson Education, Inc.




Elmasri/Navathe, Fndamentals o! Data"ase #ystems, Forth Edition Chapter 3-2

Chapter Outline

Example Database pplication !C"#P$%&E' #odel Concepts

( Entities and ttributes

( Entity )ypes, *alue +ets, and ey ttributes

( 'elationships and 'elationship )ypes ( -ea Entity )ypes

( 'oles and ttributes in 'elationship )ypes

E' Diagrams / $otation

E' Diagram or C"#P$% +chema

lternati1e $otations ( #3 class diagrams, others





E$ample C%M&'N

Data"ase

'euirements o the Company !o1ersimpliied or

illustrati1e purposes&

( )he company is organi5ed into DEP')#E$)s.Each department has a name, number and an

employee 6ho manages the department. -e eep

trac o the start date o the department manager.

( Each department controls a number o P'"7EC)s.Each pro8ect has a name, number and is located at a

single location.





E$ample C%M&'N Data"ase

(Cont)

( -e store each E#P3"%EE9s social security number,

address, salary, sex, and birthdate. Each employee

works for one department but may work on se1eral

pro8ects. -e eep trac o the number o hours per

6ee that an employee currently 6ors on each pro8ect.

-e also eep trac o the direct supervisor o each

employee.

( Each employee may have a number o DEPE$DE$)s.:or each dependent, 6e eep trac o their name, sex,

birthdate, and relationship to employee.





ER Model Concepts

Entities and ttributes ( Entities are speciic ob8ects or things in the mini/6orld that are

represented in the database. :or example the E#P3"%EE 7ohn+mith, the 'esearch DEP')#E$), the Product; P'"7EC)

( ttributes are properties used to describe an entity. :or example an

E#P3"%EE entity may ha1e a $ame, ++$, ddress, +ex,<irthDate

( speciic entity 6ill ha1e a 1alue or each o its attributes. :orexample a speciic employee entity may ha1e $ame=>7ohn +mith>,++$=>?2@4AB>, ddress =>@?, :ondren, Fouston, );>, +ex=>#>,<irthDate=>0/7$/AAG

( Each attribute has a value set !or data type& associated 6ith it ( e.g.integer, string, subrange, enumerated type, H





Types of Attributes (1)

+imple ( Each entity has a single atomic 1alue or the attribute. :or example,

++$ or +ex.

Composite ( )he attribute may be composed o se1eral components. :or example,

ddress !pt, Fouse, +treet, City, +tate, JipCode, Country& or $ame !:irst$ame, #iddle$ame, 3ast$ame&. Composition may orma hierarchy 6here some components are themsel1es composite.

#ulti/1alued ( n entity may ha1e multiple 1alues or that attribute. :or example,

Color o a C' or Pre1iousDegrees o a +)DE$). Denoted asKColorL or KPre1iousDegreesL.





Types of Attributes (2)

In general, composite and multi/1alued attributes may benested arbitrarily to any number o le1els although this is

rare. :or example, Pre1iousDegrees o a +)DE$) is a

composite multi/1alued attribute denoted by

KPre1iousDegrees !College, %ear, Degree, :ield&L.





Entity Types and Key Attributes

Entities 6ith the same basic attributes are grouped or typed into anentity type. :or example, the E#P3"%EE entity type or theP'"7EC) entity type.

n attribute o an entity type or 6hich each entity must ha1e auniue 1alue is called a ey attribute o the entity type. :orexample, ++$ o E#P3"%EE.

ey attribute may be composite. :or example, *ehicle)ag$umberis a ey o the C' entity type 6ith components !$umber, +tate&.

n entity type may ha1e more than one ey. :or example, the C'entity type may ha1e t6o eysM

( *ehicleIdentiication$umber !popularly called *I$& and ( *ehicle)ag$umber !$umber, +tate&, also no6n as licenseNplate number.


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EN*+* #E* orresponding to the

EN*+* *&E C'R

car 1!!<C ?2@, )E;+&, )B2, :ord #ustang, con1ertible, ?, !red, blac&&

car 2!!<C ?2@, $E- %"'&, -P2, $issan @00J;, 2/door, 2002, !blue&&

car @!!*+% 20, )E;+&, )D2, <uic 3e+abre, 4/door, 200@, !6hite, blue&&

.

.

.

C'

'egistration!'egistration$umber, +tate&, *ehicleID, #ae, #odel, %ear, !Color&




#UMM'R %F ER-D+'R'M

N%*'*+%N F%R ER #C.EM'##eaning

E$)I)% )%PE

-E E$)I)% )%PE

'E3)I"$+FIP )%PE

IDE$)I:%I$O 'E3)I"$+FIP )%PE

))'I<)E

E% ))'I<)E

#3)I*3ED ))'I<)E

C"#P"+I)E ))'I<)E

DE'I*ED ))'I<)E

)")3 P')ICIP)I"$ ": E2 I$ '

C'DI$3I)% ')I" ?M$ :"' E?ME2 I$ '

+)'C)'3 C"$+)'I$) !min, max& "$ P')ICIP)I"$

": E I$ '

+ymbol

E? ' E2

E? ' E2

' !min,max&

E

$




ER D+'R'M Entity *ypes are0EM&1%EE, DE&'R*MEN*, &R%2EC*, DE&ENDEN*




Relationships and Relationship

Types (1) relationship relates t6o or more distinct entities 6ith a

speciic meaning. :or example, E#P3"%EE 7ohn +mith 6orson the Product; P'"7EC) or E#P3"%EE :ranlin -ongmanages the 'esearch DEP')#E$).

'elationships o the same type are grouped or typed into a

relationship type. :or example, the -"'+N"$ relationshiptype in 6hich E#P3"%EEs and P'"7EC)s participate, or the#$OE+ relationship type in 6hich E#P3"%EEs andDEP')#E$)s participate.

)he degree o a relationship type is the number o participatingentity types. <oth #$OE+ and -"'+N"$ are binaryrelationships.




E$ample relationship instanes o! the %R4#5F%R

relationship "et6een EM&1%EE and DE&'R*MEN*

e?

e2

e@

e4

eA

eB

e

E#P3"%EE

r ?

r 2

r @

r 4

r A

r B

r

-"'+N:"'

d?

d2

d@

DEP')#E$)




E$ample relationship instanes o! the %R4#5%N

relationship "et6een EM&1%EE and &R%2EC*

e?

e2

e@

e4

eA

eB

e

r ?

r 2

r @

r 4

r A

r B

r

p?

p2

p@

r

r





Types (2)#ore than one relationship type can exist 6ith the same

participating entity types. :or example, #$OE+ and

-"'+N:"' are distinct relationships bet6een

E#P3"%EE and DEP')#E$), but 6ith dierent

meanings and dierent relationship instances.




ER D+'R'M Relationship *ypes are0%R4#5F%R, M'N'E#, %R4#5%N, C%N*R%1#,

#U&ER7+#+%N, DE&ENDEN*#5%F




Wea Entity Typesn entity that does not ha1e a ey attribute

6ea entity must participate in an identiying relationship type 6ith ano6ner or identiying entity type

Entities are identiied by the combination oM

( partial ey o the 6ea entity type

( )he particular entity they are related to in the identiying entity

typeExample:

+uppose that a DEPE$DE$) entity is identiied by the dependent9s irstname and birhtdate, and the speciic E#P3"%EE that the dependent isrelated to. DEPE$DE$) is a 6ea entity type 6ith E#P3"%EE as its

identiying entity type 1ia the identiying relationship typeDEPE$DE$)N":




ea8 Entity *ype is0 DE&ENDEN*

+denti!ying Relationship is0 DE&ENDEN*#5%F




Constraints on Relationships

Constraints on 'elationship )ypes

( ! lso no6n as ratio constraints &

( #aximum Cardinality "ne/to/one !?M?&

"ne/to/many !?M$& or #any/to/one !$M?&

#any/to/many

( #inimum Cardinality !also called participationconstraint or existence dependency constraints& 5ero !optional participation, not existence/dependent&

one or more !mandatory, existence/dependent&




Many-to-one (N09) RE1'*+%N#.+&

e?

e2

e@

e4

eA

eB

e

E#P3"%EE

r ?

r 2

r @

r 4

r A

r B

r

-"'+N:"'

d?

d2

d@

DEP')#E$)




Many-to-many (M0N) RE1'*+%N#.+&

e?

e2

e@

e4

eA

eB

e

r ?

r 2

r @

r 4

r A

r B

r

p?

p2

p@

r

r





Types (!)

-e can also ha1e a recursive relationship type.<oth participations are same entity type in dierent roles.

:or example, +PE'*I+I"$ relationships bet6een

E#P3"%EE !in role o super1isor or boss& and !another&

E#P3"%EE !in role o subordinate or 6orer&. In ollo6ing igure, irst role participation labeled 6ith ? and

second role participation labeled 6ith 2.

In E' diagram, need to display role names to distinguish

participations.




' RECUR#+7E RE1'*+%N#.+&

#U&ER7+#+%N

e?

e2

e@

e4

eA

eB

e

E#P3"%EE

r ?

r 2

r @

r 4

r A

r B

+PE'*I+I"$

2?

?2

2

?

?

?2

?

2

2

© )he <en8aminCummings Publishing Company, Inc. ?4, Elmasri$a1athe, :undamentals o Database +ystems, +econd Edition




Rersive Relationship *ype is0 #U&ER7+#+%N

(partiipation role names are sho6n)




Attributes of Relationship types

relationship type can ha1e attributesQ or

example, FoursPer-ee o -"'+N"$Q its

1alue or each relationship instance describes

the number o hours per 6ee that an

E#P3"%EE 6ors on a P'"7EC).




'ttri"te o! a Relationship *ype is0.ors o! %R4#5%N

#t t l C t i t




#trtral Constraints

one 6ay to e$press semantis

o! relationshipsStructural costraits o relatioships:

Car!ialit" ratio !o a binary relationship&M ?M?, ?M$, $M?,or #M$

S#$%& '( )*+C,& +)).$).,+/E &'E. $& /#E*,&

)articipatio costrait !on each participating entitytype&M total !called existence dependency& or partial.

S#$%& '( $'*E *,&,& /#E *,&

$")EM )hese are easy to speciy or <inary 'elationship)ypes.





'lternative (min, ma$) notation !or relationship

strtral onstraints0 +peciied on each participation o an entity type E in a relationship type '

+peciies that each entity e in E participates in at least min and at most maxrelationship instances in '

Deault!no constraint&M min=0, max=n

#ust ha1e min≤max, min≥0, max ≥?

Deri1ed rom the no6ledge o mini/6orld constraints

ExamplesM

department has exactly one manager and an employee can manage at most

one department.

( +peciy !0,?& or participation o E#P3"%EE in #$OE+

( +peciy !?,?& or participation o DEP')#E$) in #$OE+ n employee can 6or or exactly one department but a department can ha1e

any number of employees.

( +peciy !?,?& or participation o E#P3"%EE in -"'+N:"'

( +peciy !0,n& or participation o DEP')#E$) in -"'+N:"'





The ("in#"a$) notation

relationship constraints

!?,?&!0,?&

!?,$&!?,?&





C"#P$% E' +chema Diagram

using !min, max& notation





Relationships o! .igher Degree

'elationship types o degree 2 are called iar"

'elationship types o degree @ are called terar" and odegree n are called -ar"

In general, an n/ary relationship is not eui1alent to n

binary relationships

Figher/order relationships discussed urther in Chapter 4





Data Modeling *ools

number o popular tools that co1er conceptual

modeling and mapping into relational schema

design. ExamplesM E'-in, +/ Designer!Enterprise pplication +uite&, E'/ +tudio, etc.

P"+I)I*E+M ser1es as documentation o

application reuirements, easy user

interace / mostly graphics editor support

& "l ith C t





&ro"lems 6ith Crrent

Modeling *oolsDIO'##I$O

( Poor conceptual meaningul notation.

( )o a1oid the problem o layout algorithms and aesthetics

o diagrams, they preer boxes and lines and do nothing

more than represent !primary/oreign ey& relationships

among resulting tables.!a e6 exceptions&

#E)F"D"3O%

( lac o built/in methodology support. ( poor tradeo analysis or user/dri1en design preerences.

( poor design 1eriication and suggestions or impro1ement.

Some o the Curretl" +vailale +utomate! ataase





Some o the Curretl" +vailale +utomate! ataase

esi /ools

C$)+&( /$$* &C/,$&+*,/(

Emarca!ero

/echoloies

E. Stu!io ataase o!eli i E. a! ,E1

' +rtisa ataase a!miistratio a! space a! securit"maaemet

$racle eveloper 2000 a!

esier 2000

ataase mo!eli applicatio !evelopmet

)op;i Sot<are S"stem +rchitect 2001 ata mo!eli o=ect mo!eli process mo!elistructure! aal"sis>!esi

)latium/echolo"

)latium Eterpriceo!eli Suite: Er<i')%i )ara!im )lus

ata process a! usiess compoet mo!eli

)ersistece ,c )<ertier appi rom $-$ to relatioal mo!el

.atioal .atioal .ose o!eli i * a! applicatio eeratio i C??

a! @+A+

.oue %are .% etro appi rom $-$ to relatioal mo!el

.esolutio *t! case Coceptual mo!eli up to co!e maiteace

S"ase Eterprise +pplicatio Suite ata mo!eli usiess loic mo!eli

Aisio Aisio Eterprise ata mo!eli !esi a! reeieeri Aisual 'asica! Aisual C??

ER D+'R'M F%R ' :'N4





ER D+'R'M F%R ' :'N4

D'*':'#E

© )he <en8aminCummings Publishing Company, Inc. ?4, Elmasri$a1athe, :undamentals o Database +ystems, +econd Edition





&R%:1EM 6ith ER notation

)FE E$)I)% 'E3)I"$+FIP #"DE3 I$

I)+ "'IOI$3 :"'# DID $")+PP"') )FE +PECI3IJ)I"$

OE$E'3IJ)I"$ <+)'C)I"$+

E t d d E tit R l ti hi



El i/N th F d t l ! D t " # t F th Editi Ch t 3 37

E$tended Entity%Relationship

(EER) Model

Incorporates +et/subset relationships

Incorporates +peciali5ationOenerali5ation Fierarchies

$E;) CFP)E' I33+)')E+ F"- )FE E'

#"DE3 C$ <E E;)E$DED -I)F

/ +et/subset relationships and

+peciali5ationOenerali5ation Fierarchies and ho6 todisplay them in EE' diagrams

chapter 3 erd

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