02 Relational Sp 08

8/18/2019 02 Relational Sp 08

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Entity-Relationship Diagramsand the Relational Model

CS 186, Fall 2007, e!t"re 2

R # $, Chaps% 2#&

' relationship, ( thin), is li)e ashar), yo" )no*+ (t has to!onstantly moe or*ard or it dies%'nd ( thin) *hat *e got on o"rhands is a dead shar)%


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Reie*

3 .hy "se a D4MS+ 5S proidesR'M and dis)


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Reie*

3 .hy "se a D4MS+ 5S proidesR'M and dis) Con!"rren!y

Re!oery 'stra!tion, Data (ndependen!e

"ery ang"ages

E9!ien!y /or most tas)s Se!"rity

Data (ntegrity


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Data Models

3 D4MS models real *orld3 Data Model is lin)

et*een "ser:s ie* o

the *orld and itsstored in !omp"ter

3 Many models e;ist3 .e thin) in terms o%%

Relational Model /!leanand !ommon

Entity-Relationship model/design


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.hy St"dy the RelationalModel+

3 Most *idely "sed model%3 =ega!y systems> in older models

e%g%, (4M:s (MS

3 5?e!t-oriented !on!epts merged in =5?e!t-Relational> t*o ariants

3 5?e!t model )no*n to the D4MS

3 5?e!t-Relational Mapping /5RM o"tside the D4MS ' la Rails

3


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Steps in Dataase Design

3 ReA"irements 'nalysis "ser needsB *hat m"st dataase do+

3 Con!ept"al Design high leel des!ription /oten done *@ER model

Rails encourages you to work here3 ogi!al Design

translate ER into D4MS data model Rails requires you to work here too

3 S!hema Renement !onsisten!y, normaliation

3 hysi!al Design - inde;es, dis) layo"t3 Se!"rity Design - *ho a!!esses *hat, and ho*


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Con!ept"al Design

3 .hat are the entities and relationships in the enterprise+

3 .hat inormation ao"t these entities and relationships

sho"ld *e store in the dataase+

3 .hat integrity constraints or business rules hold+3 ' dataase s!hema: in the ER Model !an e represented

pi!torially /ER diagrams%

3 Can map an ER diagram into a relational s!hema%


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ER Model 4asi!s

3 Entity: Real-*orld o?e!t, disting"ishalerom other o?e!ts% 'n entity is des!ried

"sing a set o attributes%3 Entity Set G ' !olle!tion o similar entities%

E%g%, all employees% 'll entities in an entity set hae the same

set o attri"tes% /Hntil *e !onsiderhierar!hies, any*ayI

Ea!h entity set has a key (underlined)% Ea!h attri"te has a domain%

Employees

ssnname

lot


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ER Model 4asi!s /Contd%

3 RelationshipG 'sso!iation among t*o or moreentities% E%g%, 'ttishoo *or)s in harma!ydepartment%

relationships !an hae their o*n attri"tes%

3 Relationship Set G Colle!tion o similar relationships% 'n n-ary relationship set R relates n entity sets E !!! En B

ea!h relationship in R inoles entities e ∈ E, %%%, en ∈ En

lot

name

Employees

ssn

Works_In

since dname

budgetdid

Departments


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Key Constraints

'n employee!an *or) inmany

departmentsB adept !an haemanyemployees%

1-to-11-to ManyMany-to-

Many

since

Manages

dname

budgetdid

Departments

since

Works_In

lot

name

ssn

Employees

(n !ontrast, ea!hdept has at mostone manager,a!!ording to the

key constraint onMana es%


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Lto e !learL

3 Re!all that ea!h relationship hase;a!tly one element o ea!h EntitySet

=1-M> is a !onstraint on theRelationship Set, not ea!hrelationship

3 hin) o 1-M-M ternary relationship


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arti!ipation Constraints3 Does eery employee *or) in a department+3 ( so, this is a participation constraint

the parti!ipation o Employees in .or)sN(n is said to e total /s% partial .hat i eery department has an employee *or)ing in it+

3 4asi!ally means =at least one>

lot

name dname

budgetdid

sincename dname

budgetdid

since

Manages

since

DepartmentsEmployees

ssn

Works_In

MeansG =e;a!tly one


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.ea) Entities' weak entity !an e identied "niA"ely only y !onsidering the

primary )ey o another /owner entity%

5*ner entity set and *ea) entity set m"st parti!ipate in a one-to-many relationship set /one o*ner, many *ea) entities%

.ea) entity set m"st hae total parti!ipation in this identi"yingrelationship set%

lot

nameagepname

DependentsEmployees

ssn

Policy

cost

.ea) entities hae only a =partial )ey> /dashed "nder


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4inary s% ernary Relationships

( ea!h poli!y iso*ned y ?"st 1employeeG 4ad design

ene!iciary

agepname

Dependents

policyid cost

Policies

Purc"aser

name

Employees

ssn lot

4etter design

3 Think throughall the constraintsin the 2nddiagram!

Policies

policyid cost

agepname

Dependents#overs

name

Employees

ssn lot

Key constraint

on Policieswould meanpolicy can onlycover 1dependent!


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4inary s% ernary Relationships/Contd%

3 reio"s e;ample ill"strated a !ase *hen t*oinary relationships *ere etter than oneternary relationship%

3 'n e;ample in the other dire!tionG a ternaryrelation Contra!ts relates entity sets arts,

Departments and S"ppliers, and hasdes!riptie attri"te qty % Oo !omination oinary relationships is an adeA"ate s"stit"te%/.ith no ne* entity setsI


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4inary s% ernary Relationships/Contd%

S =!an-s"pply> , D =needs> , and D =deals-*ith> S does notimply that D has agreed to "y rom S%

o* do *e re!ord qty +

$uppliers

%ty

Departments#ontr actParts

$uppliers

Departments

deals-&it"

Parts

can-supply

VS.

needs


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S"mmary so ar

3 Entities and Entity Set /o;es

3 Relationships and Relationship sets/diamonds

inary

n-ary

3 Key !onstraints /1-1,1-O, M-O, arro*s

3 arti!ipation !onstraints /old or otal3 .ea) entities - reA"ire strong entity or )ey


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Relational DataaseGDenitions

3 Relational dataaseG a set o relations%3 RelationG made "p o 2 partsG

S!hema G spe!ies name o relation, pl"s

name and type o ea!h !ol"mn%3 E%g% St"dents/sidG string, nameG string, loginGstring, ageG integer, gpaG real

(nstan!e G a tale, *ith ro*s and !ol"mns%3 Pro*s Q !ardinality

3 Pelds Q degree @ arity

3 Can thin) o a relation as a set o ro*sor t"ples%

i%e%, all ro*s are distin!t


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E;G (nstan!e o St"dents Relation

sid name login age gpa

&666 ones ?onesT!s 18 &%U

&688 Smith smithTee!s 18 &%2&60 Smith smithTmath 1 &%8

3 Cardinality Q &, arity Q , all ro*s distin!t3 Do all al"es in ea!h !ol"mn o a relation instan!e

hae to e distin!t+


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S - ' lang"age or RelationalD4s

3 S /a%)%a% =SeA"el>, standardlang"age

3 Data Denition ang"age /DD

!reate, modiy, delete relations spe!iy !onstraints administer "sers, se!"rity, et!%

3 Data Manip"lation ang"age /DM Spe!iy A"eries to nd t"ples thatsatisy !riteria

add, modiy, remoe t"ples


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S 5erie*

3 CRE'E '4E VnameW / VeldW VdomainW, L

3 (OSER (O5 VnameW /Veld namesW X'HES /Veld al"esW

3 DEEE FR5M VnameW.ERE V!onditionW

3 HD'E VnameWSE Veld nameW Q Val"eW

.ERE V!onditionW

3 SEEC VeldsWFR5M VnameW

.ERE V!onditionW


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Creating Relations in S

3Creates the St"dents relation% OoteG the type /domain o ea!h eld is

spe!ied, and enor!ed y the D4MS

*heneer t"ples are added or modied%CREATE TABLE Students

(sid CHAR(20),

name CHAR(20),login CHAR(10),

age INTEGER,

ga !L"AT)


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ale Creation /!ontin"ed

3 'nother e;ampleG the Enrolledtale holds inormation ao"t!o"rses st"dents ta)e%

CREATE TABLE En#olled(sid CHAR(20),

$id CHAR(20),g#ade CHAR(2))


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Keys

3 Keys are a *ay to asso!iate t"ples indiJerent relations3 Keys are one orm o integrity

!onstraint /(C

sid name login age gpa

&666ones ?onesT!s 18 &%U

&688Smith smithTee!s 18 &%2

&60Smith smithTmath 1 &%8

sid cid grade

53666 Carnatic101 C

53666 Reggae203 B53650 Topology112 A53666 History105 B

Enrolled St"dents

R(M'RY KeyF5RE($O Key


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rimary Keys

3 ' set o elds is a s"per)ey iG Oo t*o distin!t t"ples !an hae same al"es in all

)ey elds

3 ' set o elds is a )ey or a relation i G

(t is a s"per)ey Oo s"set o the elds is a s"per)ey

3 *hat i W1 )ey or a relation+ 5ne o the )eys is !hosen /y D4' to e the primary

)ey% 5ther )eys are !alled !andidate )eys%

3 E%g% sid is a )ey or St"dents%

.hat ao"t name+

he set Zsid, gpa[ is a s"per)ey%

i d C did t K i


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rimary and Candidate Keys inS

3 ossily many candidate keys /spe!ied "sing

HO(HE, one o *hi!h is !hosen as the primary key %

3 Keys m"st e "sed !are"llyI

3 =For a gien st"dent and !o"rse, there is a single

grade%>

=St"dents !an ta)e only one !o"rse, and no t*ost"dents in a !o"rse re!eie the same grade%>

CREATE TABLE En#olled (sid CHAR(20) $id CHAR(20), g#ade CHAR(2), 4RIAR5 6E5 (sid,$id))

CREATE TABLE En#olled (sid CHAR(20) $id CHAR(20), g#ade CHAR(2),

4RIAR5 6E5 (sid), &NI7&E ($id, g#ade))

s%

F i K R ti l


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Foreign Keys, Reerential(ntegrity

3 #oreign key G Set o elds in onerelation that is "sed to reer: to at"ple in another relation% M"st !orrespond to the primary )ey o the

other relation% i)e a logi!al pointer:%

3( all oreign )ey !onstraints areenor!ed, re"erential integrity isa!hieed /i%e%, no dangling reeren!es%


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Foreign Keys in S

3 '.g. nly students listed in the "tudents relation should

%e allowed to enroll for courses. sid is a oreign )ey reerring to St"dentsG

CREATE TABLE En#olled(sid CHAR(20),$id CHAR(20),g#ade CHAR(2),

4RIAR5 6E5 (sid,$id), !"REIGN 6E5 (sid) RE!ERENCES Students )

sid cid grade

53666 Carnatic101 C

53666 Reggae203 B

53650 Topology112 A

53666 History105 B

Enrolled

sid name login age gpa&666ones ?onesT!s 18 &%U

&688Smith smithTee!s 18 &%2

&60Smith smithTmath 1 &%8

St"dents

11111 English102


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Enor!ing Reerential (ntegrity

3 Consider St"dents and EnrolledB sid in Enrolled is aoreign )ey that reeren!es St"dents%

3 .hat sho"ld e done i an Enrolled t"ple *ith anon-e;istent st"dent id is inserted+ /Re$ect it%

3 .hat sho"ld e done i a St"dents t"ple is deleted+ 'lso delete all Enrolled t"ples that reer to it+ Disallo* deletion o a St"dents t"ple that is reerred to+ Set sid in Enrolled t"ples that reer to it to a de"ault sid+

/(n S, alsoG Set sid in Enrolled t"ples that reer to it to aspe!ial al"e null& denoting 'unknown or 'inapplicable %

3 Similar iss"es arise i primary )ey o St"dents t"pleis "pdated%


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(ntegrity Constraints /(Cs

3 (CG !ondition that m"st e tr"e or any instan!eo the dataaseB e%g%, domain constraints! (Cs are spe!ied *hen s!hema is dened% (Cs are !he!)ed *hen relations are modied%

3 ' legal instan!e o a relation is one that

satises all spe!ied (Cs% D4MS sho"ld not allo* illegal instan!es%

3 ( the D4MS !he!)s (Cs, stored data is moreaith"l to real-*orld meaning%

'oids data entry errors, tooI


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.here do (Cs Come From+

3 (Cs are ased "pon the semanti!s o the real-*orld that is eing des!ried in the dataaserelations%

3 .e !an !he!) a dataase instan!e to see i an

(C is iolated, "t *e !an OEXER iner that an(C is tr"e y loo)ing at an instan!e% 'n (C is a statement ao"t all possile instan!esI

From e;ample, *e )no* name is not a )ey, "t theassertion that sid is a )ey is gien to "s%

3 Key and oreign )ey (Cs are the most !ommonBmore general (Cs s"pported too%

3 (n the real *orld, sometimes the !onstraintsho"ld hold "t doesn:t --W data !leaningI


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Relational "ery ang"ages

3 ' ma?or strength o the relational modelGs"pports simple, po*er"l querying o data%

3 "eries !an e *ritten int"itiely, and theD4MS is responsile or e9!ient eal"ation% he )eyG pre!ise semanti!s or relational A"eries%

'llo*s the optimier to e;tensiely re-orderoperations, and still ens"re that the ans*er doesnot !hange%


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he S "ery ang"age

3 he most *idely "sed relational A"erylang"age% C"rrent std is SG200&B S2 is a asi!

s"set

3 o nd all 18 year old st"dents, *e !an*riteGSELECT 8 !R" Students S HERE S/age31+

3 o nd ?"st names and logins, repla!e the rst lineG

SELECT S/name, S/login

sid name age gpa

&666ones 18 &%U&688

Smith

18

&%2

&60Smith

login

?onesT!ssmithTee

smithTmath1 &%8


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"erying M"ltiple Relations

3 .hat does the ollo*ing A"ery!omp"te+SELECT S/name, E/$id

!R" Students S, En#olled E HERE S/sid3E/sid AN E/g#ade39A9

sid cid grade

53831 Carnatic101 C

53831 Reggae203 B

53650 Topology112 A53666 History105 B

$ien the ollo*inginstan!e o Enrolled

S.name .cid

Smit! Topology112*e getG


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Semanti!s o a "ery

3 ' conceptual ealuation method or the preio"sA"eryG

1% do FR5M !la"seG !omp"te cross-product o St"dentsand Enrolled

2% do .ERE !la"seG Che!) !onditions, dis!ard t"ples thatail

&% do SEEC !la"seG Delete "n*anted elds3 Rememer, this is conceptual% '!t"al eal"ation

*ill e much more e9!ient, "t m"st prod"!e thesame ans*ers%


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Relational ModelG S"mmary

3 ' ta"lar representation o data%3 Simple and int"itie, !"rrently the most *idely

"sed 5?e!t-relational s"pport in most prod"!ts


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$5SH4


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Dataases or rogrammers

3 rogrammers thin) ao"t o?e!ts/str"!ts Oested and interleaed

3 5ten *ant to =persist> these things3 5ptions

en!ode opaA"ely and store

translate to a str"!t"red orm3 relational D4,


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\YHCKII

3 o* do ( =relationalie> my o?e!ts+3 ae to *rite a !onerter or ea!h

!lass+

3 hin) ao"t *hen to sae thingsinto the D4+

3 $ood ne*sG Can all e a"tomated

.ith arying amo"nts o tro"le


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5?e!t-Relational Mappings

3 Ro"ghlyG Class ] Entity Set

(nstan!e ] Entity

Data memer ] 'ttri"te Reeren!e ] Foreign Key


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Details, details

3 .e hae to map this do*n to tales3 .hi!h tale holds *hi!h !lass o

o?e!t+

3 .hat ao"t relationships+3 Sol"tion P1G De!laratie Cong"ration

.rite a des!ription le /oten in


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R"y on Rails

3 R"yG an 55 s!ripting lang"age and a pretty ni!e one, too

3 RailsG a rame*or) or *e apps

=!onention oer !ong"ration>3 great or standard *e-app st"JI

allo*s oerriding as needed

3 Xery ER-li)e


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Rails and ER

3 Models Employees

Departments

lot

name

Employees

ssn

Works_In

sincedname

budgetdid

Departments


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Some Rails =Models>

app/models/state.rb$lass State : A$ti;eRe$o#d : A$ti;eRe$o#d


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F"rther Reading

3 Chapter 18 /thro"gh 18%& in *gile+eb Deelopment with Rails

02 Relational Sp 08

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