Comp 521 f 14 Lecture 03

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Comp 521 Files and Databases Fall 2014 1

The RelationalModel

Chapter 3

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Why the Relational Model?

Most widely used model by industry. IM! In"ormi#! Mi$roso"t! %ra$le! &ybase! My&'(!

)ost*res! &+lite! ,i-e...

It is simple! ele*ant! and e""i$ient

ntities and relations are represented as tables /ables allow "or arbitrary re"eren$in*

/ables $an re"er to other tables

e$ent $ompetitor obe$toriented model %be$t&tore! 6ersant! %ntos

7 synthesis emer*in* object-relational model8 )ost*res! In"ormi#! 9ni&'(! %2! %ra$le! D2

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Relational Database: Definitions

Relational database:a set o" relations Relation:made up o" 2 parts

Instance a table!with rows and $olumns.:rows ; cardinality! :"ields ; degree /arity.

Schema spe$i"iesname o" relation! plus aname and type "or ea$h $olumn.

8 e.*. &tudentssid strin*! name strin*! loginstrin*! age inte*er! ga real.

Can thin< o" a relation as a set o" rowsor t!les.

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"#amle Instance of St!dents Relation

sid name lo*in a*e *pa

53=== >ones ones?$s 1@ 3.4

53=@@ &mith smith?$s 1@ 3.2

53=50 &mith smith?math 1A 3.@

Cardinality ; 3! de*ree ; 5

7ll rows in a relation instan$e ha$e tobe distinct ea$h relation is de"ined tobe a set o" uni+ue tuples

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Relational %!ery &ang!ages

7 maor stren*th o" the relational modelis that it supports simple and power"ul'!eryingo" data.

%"ten declarati$e instead o" imerati$e 'ueries $an be written intuiti-ely! and

the DM& is responsible "or e""i$iente-aluation. )re$ise semanti$s "or relational +ueries.

7llows the optimiBer to e#tensi-ely reorderoperations! and still ensure that the answerdoes not $han*e.

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Comp 521 Files and Databases Fall 2014 =

The S%& %!ery &ang!age

De-eloped by IM &ystem in the 1A0s eed "or a standard sin$e it is used by many

-endors

&tandards

&'(@=

&'(@A minor re-ision

&'(A2 maor re-ision

&'(AA maor e#tensions! almost current std

&'(03adds EM( and M! a

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Comp 521 Files and Databases Fall 2014

The S%& %!ery &ang!age

/o "ind all 1@ year old students! we $anwrite

&(C/

F%M &tudents &J, &.a*e;1@

8/o "ind ust names and lo*ins! repla$e the "irst line

8Jhen a relation is re"eren$ed only on$e!the use o" -ariables is optional

&(C/ &.name! &.lo*in


53=== >ones ones?$s 1@ 3.4

53=@@ &mith smith?$s 1@ 3.2

G&H in thise#pressionindi$ates a"ormal -ariablewhi$h ta

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Comp 521 Files and Databases Fall 2014 @

""e$ti-ely G>oinsH or $onne$ts two tables

%!erying M!ltile Relations

Jhat does the"ollowin* +uery$omputeK

&(C/ &.name! .$idF%M &tudents &! nrolled J, S.sid=E.sid7D.*rade;G7H

sid cid grade

53688 Carnatic101 C

53688 Reggae203 B

53650 Topology112 A53666 History105 B

i-en the "ollowin*

instan$es o" nrolled and&tudents

S.name E.cid

Smit Topology

we *et


53=== >ones ones?$s 1@ 3.4

53=@@ &mith smith?$s 1@ 3.2


St!dents"

Enrolled"

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Destroying and )ltering Relations

Destroys the relation &tudents. /hes$hema in"ormation andthe tuples aredeleted.

D%) /7( &tudents

/he s$hema o" &tudents is altered by

addin* a new "ieldL e-ery tuple in the$urrent instan$e is e#tended with a n!ll-alue in the new "ield.

7(/ /7( &tudents7DD C%(9M"irstear inte*er

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)dding and Deleting T!les

Can insert a sin*le tuple usin*

I&/ I/% &tudents sid! name! lo*in! a*e! *pa67(9& 53=5! N&mithO! Nsmith?physO! 1@! 3.5

Can delete all tuples satis"yin* some$ondition e.*.! name ; &mith

D(/F%M&tudents &

J,&.name ; N&mithO

*o+erf!l $ariants of these commands are a$ailable, more later

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Modifying "#isting T!les

Can modi"y all tuples satis"yin* some$ondition e.*.! $han*e &mithPs name to

>ones

9)D7/ students&/ name ; P>onesPJ, name ; P&mithPL

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Integrity (onstraints I(s

IC$ondition that must be true "or anyinstan$e o" the databaseL e.*.! domainconstraints. ICs are spe$i"ied when s$hema is de"ined.

ICs are $he$

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*rimary 0ey (onstraints

7 set o" "ields is a 1ey"or a relation i" 1. o two tuples $an ha-e same -alues in

all

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*rimary and (andidate 0eys in S%&

)ossibly many candidate 1eys spe$i"ied usin*9I'9! one o" whi$h is $hosen as therimary1ey.

C7/ /7(nrolled sid C,720

$id C,720! *rade C,72! )IM7 T sid!$id

GFor a *i-en student and $ourse!there is a sin*le *rade.H -s.

G&tudents $an ta

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Comp 521 Files and Databases Fall 2014 1=

3oreign 0eys2 Referential Integrity

3oreign 1ey &et o" "ields in one relation that isused to Gre"eren$eH a tuple in another relation.Must $orrespond to primary

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3oreign 0eys in S%&

%nly students listed in the &tudents relationshould be allowed to enroll "or $ourses.

C7/ /7(nrolled sid C,720! $id C,720! *rade C,72!

)IM7 T sid!$id! F%I T sid FC&&tudents


53=== >ones ones?$s 1@ 3.453=@@ &mith smith?$s 1@ 3.2


sid cid grade

53688 Carnatic101 C

53688 Reggae203 B

53650 Topology112 A53666 History105 B

nrolled&tudents

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Comp 521 Files and Databases Fall 2014 1@

"nforcing Referential Integrity

Consider &tudents and nrolledL sidin nrolled is a"orei*n

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Comp 521 Files and Databases Fall 2014 1A

Referential Integrity in S%&

&'(UA2 and &'(1AAAsupport all 4 options ondeletes and updates.

De"ault is % 7C/I%

delete/!date isrejected C7&C7D also delete

all tuples that re"er todeleted tuple

&/ 9(( U&/ DF79(/sets "orei*n

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Where do I(s (ome 3rom?

ICs are based upon the semanti$s o" therealworld enterprise that is bein*des$ribed in the database relations.

Je $an $he$< a database instan$e to see i"

an IC is -iolated! but we $an 6in"erthat an IC is true by loo

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&ogical D6 Design: "R to Relational

ntity sets to tables

C7/ /7(

mployeesssn C,711!name C,720!lot I/!)IM7 T ssnEmployees

ssn

name

lot

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Relationshi Sets to Tables

In translatin* arelationship set to arelation! attributes o" therelation must in$lude

Teys "or ea$hparti$ipatin* entity setde$lared as "orei*n

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Re$ie+: 0ey (onstraints

a$h dept has atmost one mana*er!a$$ordin* to the1ey constraint onMana*es.

Translation to

relational model?

Many-to-Many1-to-1 1-to Many Many-to-1

Employees

ssn

name

lot

(epartments

did

dname

)!dget

&anages

since

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Translating "R Diagrams +ith 0ey (onstraints

Map relationshipto a table ote that didis

the

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Re$ie+: *articiation (onstraints

Does e-ery department ha-e a mana*erK I" so! this is aarticiation constraint the parti$ipation o"

Departments in Mana*es is said to be total-s.artial.

-ery did-alue in Departments table must appear in a row o"the Mana*es table with a nonnull ssn-alue

Employees

ssn

name

lot

(epartments

did

dname

)!dget

*or$s+,n

since

&anages

since

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*articiation (onstraints in S%&

Je $an $apture parti$ipation $onstraints in-ol-in*one entity set in a binary relationship! but littleelse without resortin* to C,CT$onstraints.

C7/ /7( DeptVM*r

did I/! dname C,720! bud*et 7(! ssn C,711 %/ 9((! sin$e D7/!

)IM7 T did! F%I T ssn FC&mployees! % D(/ % 7C/I%

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Re$ie+: Wea1 "ntities

7 +ea1 entity $an be identi"ied uni+uely only by$onsiderin* the primary

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Comp 521 Files and Databases Fall 2014 2@

Translating Wea1 "ntity Sets Jea< entity set and identi"yin* relationship

set are translated into a sin*le table.

Jhen the owner entity is deleted! all ownedwea< entities are also be deleted.

C7/ /7( DepV)oli$y pname C,720! a*e I/! $ost 7(! ssn C,711 %/ 9((!

)IM7 T pname! ssn! F%I T ssn FC&mployees! % D(/ C7&C7D

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Comp 521 Files and Databases Fall 2014 2A

Re$ie+: IS) 7ierarchies

8$erla constraints Can >oe be an ,ourlyVmps as wellas a Contra$tVmps entityK )llo+ed/disallo+ed

(o$ering constraints Does e-ery mployees entity alsoha-e to be an ,ourlyVmps or a Contra$tVmps entityK9es/no

Employees

ssn name

lot

Ho!rly+Emps

Ho!rly+.age

Ho!rs+.or$ed

Contract+emps

salary,SA

It is o"ten use"ul tosubdi-ide entities into$lasses! li

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Translating IS) 7ierarchies to Relations

General approach: 3 relations mployees! ,ourlyVmps and

Contra$tVmps.

8 7o!rly"ms -ery employee is re$orded inmployees. For hourly emps! e#tra in"o re$orded in,ourlyVmps ho!rly+ages! ho!rs+or1ed! ssnLmust delete ,ourlyVmps tuple i" re"eren$edmployees tuple is deleted.

8 'ueries in-ol-in* all employees easy! those in-ol-in*ust ,ourlyVmps re+uire a oin to *et some attributes.

7lternati-e >ust ,ourlyVmps and Contra$tVmps. 7o!rly"ms ssn! name2 lot2 ho!rly+ages2

ho!rs+or1ed. a$h employee must be in one o" these two sub$lasses.

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Re$ie+: 6inary $s. Ternary Relationshis

e$all whatwere theadditional$onstraints

implied bythe thebetterdesi*nK

ad desi*n

Employees

ssn name lot

(ependents

pname age

Co/ers

-olicies

costpolicyid

etter desi*n

(ependents

pname age

Employees

ssn

namelot

-!rcaser Bene0iciary

-olicies

costpolicyi

d

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6inary $s. Ternary Relationshis (ontd.

Tey $onstraintsallow us to$ombine )ur$haserwith )oli$ies! andene"i$iary withDependents.

)arti$ipation$onstraints leadto %/ 9(($onstraints.

Jhat i" )oli$ies is awea< entity setK*eneri$ poli$ynumbers

C7/ /7( )oli$ies poli$yid I/! $ost 7(! ssn C,711 %/ 9((! )IM7 T poli$yid. F%I T ssn FC& mployees! % D(/ C7&C7D

C7/ /7( Dependents pname C,720! a*e I/! poli$yid I/! )IM7 T pname! poli$yid. F%I T poli$yid FC& )oli$ies! % D(/ C7&C7D

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;ie+s

7 $ie+is ust a relation! but we store adefinition! rather than a set o" tuples.

C7/ 6IJoun*7$ti-e&tudents name! *rade7& &(C/ &.lo*in! .*rade

F%M &tudents &! nrolled J, &.sid ; .sid and &.a*eW21

6iews $an be dropped usin* the D%) 6IJ$ommand.

,ow to handle D%) /7(i" thereOs a -iew on the tableK8 D%) /7($ommand has options to let the user spe$i"y

this.

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;ie+s to s!ort IS) relations

/he $ommon elements o" an I&7 hierar$hy$an be supported usin* -iews.

For e#ample! $onsider this implementationo" 7lternate 2 "rom slide 30

C7/ 6IJ mployeessn! name! lot7& &(C/ ,.ssn! ,.name! ,.lotF%M ,ourlyVmps9I%

&(C/ C.ssn! C.name! C.lotF%M Contra$tVmps

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;ie+s and Sec!rity

6iews $an be used to present ne$essaryin"ormation or a summary! while hidin*details in underlyin* relations.

i-en oun*&tudents! but not &tudents or

nrolled! we $an "ind students who ha-e areenrolled! but not their sid5s! cid5s2 or e-en theira*es.

lo*in *rade

smith?$s C

smith?$s smith?math 7

ones?$s

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Relational Model: S!mmary

7 tabular representation o" data. &imple and intuiti-e! $urrently the most widely

used.

Inte*rity $onstraints $an be spe$i"ied by theD7! based on appli$ation semanti$s. DM&$he$

Comp 521 f 14 Lecture 03

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