chapter 04 database learning skills

7/26/2019 Chapter 04 Database Learning Skills

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Introduction to

DatabasesChapter 4:Designing aDatabase


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Designing Relational

TablesTypical process for converting E-Rdiagrams to relational tables: Each entity converts to table

For many-to-many relationships, each

associative entity converts to table Attribtes become table colmns

Ensre foreign !eys appear in proper placesin tables

To convert single entity, create table ofsame name "ith colmn for eachattribte


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Salesperson Entity and

Table


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Converting Binary

Relationships #reater importance in selectingidenti$er and primary !ey

%denti$er and primary !ey de$ne foreign

!ey that establishes relationshipsbet"een tables

&ften more than one "ay torepresent entity relationships as

relational tables


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Example: Converting ! BinaryRelationship


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Example: Converting ! Binary Relationship


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'onverting one-to-one(alesperson)&*ce relationship

&ptions:

'onvert relationship tosingle)combined table

'onvert relationship to t"o tables


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'onsiderations: +siness environment considers

(alesperson and &*ce as separateentities

odality of ero at (alesperson entity inE-R diagram .o*ce may have no oneassigned/

(alesperson entity in E-R diagram has

relationships "ith other entities


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(oltion 0:

'ombine t"o entities into one table


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(oltion 1: T"o separate tables &*ce 2mber as foreign !ey in

(alesperson table


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(oltion 3:

T"o separate tables

(alesperson 2mber as foreign !ey in

&*ce table


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Example: Converting !" BinaryRelationship


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Each occrrence of (alesperson isrelated to ero or more occrrencesof 'stomer

4ni5e identi$er of entity on 6one7side is placed as foreign !ey in entityof 6many7 side


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Example: Converting "!" BinaryRelationship


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ost relational D+( systems do notdirectly spport many-to-manyrelationships

(oltion: %nclde associative entity toestablish relationship

ay se composite !ey as primary!ey in associative entity


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Example: Converting ! #naryRelationship


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Example: Converting ! #naryRelationship

8ith:

&nly one entity type involved, and

&ne-to-one relationship

'onversion re5ires only one table


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Example: Converting !" #naryRelationship


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Example: Converting !" #naryRelationship


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Example: Converting "!" #naryRelationship

any-to-many nary relationship:

For e9ample: one prodct can beconstrcted ot of set or sbset of otherprodcts

#eneral rle in conversion: 2mber of tables e5al to nmber of entity

types pls one more table for many-to-manyrelationship

- nary relationship - 1 tables - binary relationship - 3 tables

- ternary relationship - for tables


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Example: $ood ReadingBoo%stores


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&ormali'ing Data

Data normaliation:ethodology fororganiing attribtes into tables toeliminate redndancy among non!ey

attribtes #oals:

Each resltant table describes single entitytype or single many-to-many relationship

Foreign !eys appear e9actly "here needed ;roperly strctred relational database


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&ormali'ation

Techni(ues T"o types of inpt needed for datanormaliation process

0< =ist of all attribtes to be incorporated indatabase, inclding intersection data attribtes

1< =ist of fnctional dependencies: all de$ningassociations bet"een attribtes

%n fnctional dependencies, oneattribte .determinate attribte/

de$nes vale of another attribte(alesperson 2mber > (alesperson 2ame


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Salesperson Entity )ttributes


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Salesperson Entity *unctional Dependencies


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Example: De+ning )ttributes and *unctionalDependencies

?antity is de$ned by t"o combinedattribtes

anager is de$ned independently by

t"o attribtes Department 2mber and (alesperson

2mber

(alesperson 2mber also de$nes

Department 2mber


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&ormali'ing Data

2ormal forms: Rles for data normaliation

Three main normal forms First normal form

(econd normal form

Third normal form 2ormaliation:

4ses normal forms to step throgh 6decompositionprocess7 that decomposes attribtes into sbgrops

%n third normal form, grop of tables is

"ell-strctred relational database "ith nodata redndancy


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&ormali'ing Data

First normal form: Eliminates mltiple vales

(econd normal form: Eliminates partial ,unctional dependencies

.data dependent on part of primary !ey/

Every non!ey attribte mst be fllyfnctionally dependent on entire !ey of table

Third normal form: Eliminates transitive dependencies .one

non!ey attribte is fnctionally dependent onanother/

2on!ey attribtes are not allo"ed to de$neother non!ey attribtes


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Example: #nnormali'ed

Data


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*irst &ormal *orm


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Second &ormal *orm


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Third &ormal *orm


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Denormali'ing Data

Denormaliing may be needed "hen:

2ormaliation has been ta!en to e9tremeToo many small tables creating more "or! and

storage space

E


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Summary

%n converting E-R diagrams to relationaltables, each entity typically converted intotable, "ith attribtes as table colmns

chapter 04 database learning skills

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