AIS relational databases

8/19/2019 AIS relational databases

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Copyright © Pearson Education Limited 2015.

Relational Databases

Chapter

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Learning Objectives

" E#plain the importance and ad$antages o% databases& as 'ell as thedi%%erence bet'een database and %ile!based legacy systems.

" E#plain the di%%erence bet'een logical and physical $ie's o% adatabase.

" E#plain %undamental concepts o% database systems such as D()*&schemas& the data dictionary& and D()* languages.

" Describe 'hat a relational database is and ho' it organi+es data.

" Create a set o% 'ell!structured tables to properly store data in arelational database.

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INTRODUCTION

" Relational databases underlie most modernintegrated ,-*s. /hey are the most popular type o% database used

%or transaction processing. -n this chapter& 'ell de%ine the concept o% a

database.


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What Is a Database?

" E%%iciently and centrally coordinates in%ormation %or arelated group o% %iles

" , %ile is a related group o% records

" , record is a related group o% %ields" , %ield is a speci%ic attribute o%

interest %or the entity record

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FILE VS. DATAASES" Lets e#amine some basic principles about ho' data are

stored in computer systems. ,n entity is anything about 'hich the organi+ation 'ishes to

store data. ,t your college or uni$ersity& one entity 'ould be thestudent.

STUDENTS

Student ID Last Name First NamePhone

Number Birth Date

333-33-3333 Simpson Alice 333-3333 10/11/84

111-11-1111 Sanders Ned 444-4444 11/24/86

123-45-6789 Moore Artie 555-5555 04/20/85


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FILE VS. DATAASES -n%ormation about the attributes o% an entity e.g.&

the students -D number and birth date are stored in fields.

STUDENTS


Number Birth Date

333-33-3333 Simpson Alice 333-3333 10/11/84

111-11-1111 Sanders Ned 444-4444 11/24/86

123-45-6789 Moore Artie 555-5555 04/20/85


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FILE VS. DATAASES ,ll the %ields containing data about one entity e.g.&

one student %orm a record . /he e#ample belo' sho's the record %or ,rtie )oore.

STUDENTS


Number Birth Date

333-33-3333 Simpson Alice 333-3333 10/11/84

111-11-1111 Sanders Ned 444-4444 11/24/86

123-45-6789 Moore Artie 555-5555 04/20/85


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FILE VS. DATAASES

, set o% all related records %orms a file e.g.& thestudent %ile.

-% this uni$ersity only had three students and %i$e %ields%or each student& then the entire %ile 'ould be depicted

belo'.STUDENTS


Number Birth Date

333-33-3333 Simpson Alice 333-3333 10/11/84

111-11-1111 Sanders Ned 444-4444 11/24/86

123-45-6789 Moore Artie 555-5555 04/20/85


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FILE VS. DATAASES , set o% interrelated& centrally coordinated %iles %orms

a database.

*tudent4ile

Class4ile

,d$isor4ile


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FILE VS. DATAASES

" /his proli%eration o% master%iles created problems 6%ten the same in%ormation 'as

stored in multiple master %iles.

)ade it more di%%icult toe%%ecti$ely integrate data andobtain an organi+ation!'ide $ie'o% the data.

,lso& the same in%ormation maynot ha$e been consistent bet'een

%iles. -% a student changed his phonenumber& it may ha$e beenupdated in one master %ile butnot another.

)aster 4ile 14act , 4act (4act C

)aster 4ile 24act , 4act D4act 4

)aster 4ile 14act , 4act (

4act 4

EnrollmentProgram

4inancial ,idProgram

7radesProgram


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FILE VS. DATAASES

" , database is a set o%inter!related& centrallycoordinated %iles.

Database4act , 4act (4act C 4act D4act E 4act 4

EnrollmentProgram


7radesProgram

Database)anagement

*ystem


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FILE VS. DATAASES

" /he database approachtreats data as anorgani+ational resourcethat should be used byand managed %or theentire organi+ation& not 8ust a particulardepartment.

" , databasemanagement system

(DBMS) ser$es as theinter%ace bet'een thedatabase and the $ariousapplication programs.


EnrollmentProgram


7radesProgram

Database)anagement

*ystem


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FILE VS. DATAASES

" /he combination o%the database& theD()*& and the

application programsthat access thedatabase is re%erred toas the database

system.


EnrollmentProgram


7radesProgram

Database)anagement

*ystem


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FILE VS. DATAASES

" /he personresponsible %or thedatabase is thedatabaseadministrator .

" ,s technologyimpro$es& many largecompanies arede$eloping $ery largedatabases called datawarehouses.


EnrollmentProgram


7radesProgram

Database)anagement

*ystem


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I!"ORTANCE AND ADVANTA#ES OF DATAASE

S$STE!S" Database technology is e$ery'here.

)ost ne' ,-*s implement a database approach.

9irtually all main%rame computer sites usedatabase technology.

:se o% databases 'ith PCs is gro'ing also.


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S$STE!S" ,s accountants& you are li;ely to audit or 'or;

%or companies that use database technology tostore& process& and report accountingtransactions. )any accountants 'or; directly 'ith databases and

'ill enter& process& and


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S$STE!S" Database technology pro$ides the %ollo'ing bene%its to organi+ations Data integration

Data sharing Reporting %le#ibility

)inimal data redundancy and inconsistencies

Data independence

Central management o% data Cross!%unctional analysis


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S$STE!S" /he importance o% good data

(ad data leads to (ad decisions

Embarrassment

,ngry users

Data =arehousing -nstitute estimates that dirtydata costs >?00 billion per year in unnecessarypostage& mar;eting costs& and lost customer

credibility.


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DATAASE S$STE!S

" Logical and physical views of data -n %ile!oriented systems& programmers must ;no'

the physical location and layout o% records used by

a program. /hey must re%erence the location& length& and %ormat

o% e$ery %ield they utili+e.

=hen data is used %rom se$eral %iles& this process becomes more comple#.


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DATAASE S$STE!S

" Database systems o$ercome this problem byseparating the storage and use o% data elements. /'o separate $ie's o% the data are pro$ided

Logical $ie' Physical $ie'

Separating these views facilitatesapplication development, because

programmers can focus on coding the logicand not be concerned with storage details.


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Database

Logical View—User Logical View—User B

D()*

6perating

*ystem

The DB!S translatesusers" logical #iews

into instructions as to

which data should be

retrie#ed $rom the

database%

Enrollment b& 'lass*cholarship Distribution

4r.

5@*oph.

2@

Ar.

3B@

*r.

33@


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Database

Enrollment b& 'lass

Logical View—User Logical View—User B

D()*

6perating

*ystem

The o(erating s&stem

translates DB!S

re)uests into

instructions to

(h&sicall& retrie#e

data $rom #arious

dis*s%

*cholarship Distribution4r.

5@*oph.

2@

Ar.

3B@

*r.

33@


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DATAASE S$STE!S

" /he D()* handles the lin; bet'een the physicaland logical $ie's o% the data. ,llo's the user to access&


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DATAASE S$STE!S

" *eparating the logical and physical $ie's o% dataalso means users can change theirconceptuali+ations o% the data relationships 'ithout ma;ing changes in the physical storage.

" /he database administrator can also change thephysical storage o% the data 'ithout a%%ecting

users or application programs.


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DATAASE S$STE!S

" Schemas , schema describes the logical and physical

structures o% a database.

/here are three le$els o% schema. Conceptual level

• /he organi+ation!'ide $ie' o% the entire databasei.e.& the big picture.

• Lists all data elements and the relationships bet'een them.


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DATAASE S$STE!S" Schemas

, schema describes the logical and physicalstructures o% a database.

/here are three le$els o% schema. Conceptual le$el

External level

• , set o% indi$idual user $ie's o% portions o% thedatabase& i.e.& ho' each user sees the portion o%the system 'ith 'hich he interacts.

• /hese indi$idual $ie's are re%erred to assubschema.


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DATAASE S$STE!S

" Schemas , schema describes the logical and physical

structures o% a database.

/here are three le$els o% schema. Conceptual le$el

E#ternal le$el

Internal level

• , lo'!le$el $ie' o% the database.

• -t describes ho' the data are actuallystored and accessed including

– Record layouts – De%initions

– ,ddresses

– -nde#es


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Subschema++User Subschema++User B Subschema++User '

Enroll

CashReceipt

Classes *tudent

Student ,ecord 'lass ,ecord

Student No --c!aracter "9# $lass Name --c!aracter "9#

Student Name --c!aracter "26# %ept No --inte&er "4#' non-null' inde()item(

SA* Score --inte&er "2#' non-null' inde()item( $ourse No --inte&er "4#' non-null' inde()item(

!a((ing e-ternal+le#el #iews to conce(tual+le#el schema

!a((ing conce(tual+le#el items to internal+le#el descri(tions

*mith . . . , Aones . . . (

,rnold . . .D


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Subschema++User Subschema++User B Subschema++User '

Enroll

CashReceipt

Classes *tudent

Student ,ecord 'lass ,ecord

Student No --c!aracter "9# $lass Name --c!aracter "9#

Student Name --c!aracter "26# %ept No --inte&er "4#' non-null' inde()item(

SA* Score --inte&er "2#' non-null' inde()item( $ourse No --inte&er "4#' non-null' inde()item(

!a((ing e-ternal+le#el #iews to conce(tual+le#el schema

!a((ing conce(tual+le#el items to internal+le#el descri(tions

The

bidirectional

arrowsre(resent

ma((ings

between the

schema%

*mith . . . , Aones . . . (

,rnold . . .D


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DATAASE S$STE!S" /he D()* uses the mappings to translate a

re


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DATAASE S$STE!S

" ,ccountants are %re


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Database Users an% Designers

" Di%%erent users o% the database in%ormation areat an e#ternal le$el o% the database. /hese usersha$e logical views o% the data.

" ,t an internal le$el o% the database is thephysical view o% the data 'hich is ho' the datais actually physically stored in the system.

" Designers o% a database need to understand

users needs and the conceptual le$el o% theentire database as 'ell as the physical $ie'.

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Database Design

" /o design a database& you need to ha$e aconceptual $ie' o% the entire database. /heconceptual $ie' illustrates the di%%erent %iles and

relationships bet'een the %iles.

" /he data dictionary is a blueprint o% thestructure o% the database and includes dataelements& %ield types& programs that use the dataelement& outputs& and so on.

!?


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DATAASE S$STE!S

" The data dictionary , ;ey component o% a D()* is the data

dictionary. Contains in%ormation about the data elements in the

database such as meaning& relationships to otherdata& origin& usage& and %ormat.

4or each data element& there is a corresponding

record in the data dictionary describing thatelement.


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DATAASE S$STE!S

" -n%ormation pro$ided %or each element includes , description or e#planation o% the element.

/he records in 'hich it is contained.

-ts source. /he length and type o% the %ield in 'hich it is stored.

/he programs in 'hich it is used.

/he outputs in 'hich it is contained.

/he authori+ed users o% the element. 6ther names %or the element.


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DATAASE S$STE!S• ,ccountants should participate in the

de$elopment o% the data dictionary because theyha$e a good understanding o% the data elements

in a business organi+ation& as 'ell as 'herethose elements originate and ho' they are used.


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DATAASE S$STE!S

" /he D()* usually maintains the datadictionary. -t is o%ten one o% the %irst applications o% a ne'ly

implemented database system. -nputs to the dictionary include

Records o% ne' or deleted data elements. Changes in names& descriptions& or uses o% e#isting elements.

6utputs include Reports that are use%ul to programmers& database designers&

and -* users in Designing and implementing the system. Documenting the system. Creating an audit trail.


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DATAASE S$STE!S

" !"S Languages E$ery D()* must pro$ide a means o%

per%orming the three basic %unctions o% Creating a database Changing a database Fuerying a database


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DATAASE S$STE!S" Creating a database

/he set o% commands used to create the databaseis ;no'n as data definition language (DDL).DDL is used to (uild the data dictionary -nitiali+e or create the database Describe the logical $ie's %or each indi$idual user or

programmer

*peci%y any limitations or constraints on securityimposed on database records or %ields


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DATAASE S$STE!S" Changing a database

/he set o% commands used to change the databaseis ;no'n as data manipulation language

(DML). D)L is used %or maintaining the dataincluding :pdating data

-nserting data

Deleting portions o% the database


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DATAASE S$STE!S" Fuerying a database

/he set o% commands used to


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DATAASE S$STE!S" Report =riter

)any D()* pac;ages also include a report writer &a language that simpli%ies the creation o% reports.

:sers typically speci%y =hat elements they 'ant printed

Go' the report should be %ormatted

/he report 'riter then *earches the database

E#tracts speci%ied data Prints them out according to speci%ied %ormat


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DATAASE S$STE!S

" :sers typically ha$e access to both DFL andreport 'riter.

" ,ccess to DDL and D)L are typically restricted

to employees 'ith administrati$e andprogramming responsibilities.


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RELATIONAL DATAASES

" , D()* is characteri+ed by the type o% logicaldata model on 'hich it is based. , data model is an abstract representation o%

the contents o% a database. )ost ne' D()*s are called relational

databases because they use the relational modelde$eloped by E. 4. Codd in 1HI0.


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RELATIONAL DATAASES

" /he relational data model representse$erything in the database as being stored in the%orms o% tables a;a& relations.

" /his model only describes ho' the data appear in the conceptual! and e#ternal!le$el schemas.

" /he data are physically stored according to thedescription in the internal!le$el schema.


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Each row is

called a tu(le.

which rh&mes

with /cou(le%0

E h


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Each row

contains data

about a s(eci$ic

occurrence o$

the t&(e o$ entit&in the table%


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Each column in

a table contains

in$ormation

about a s(eci$icattribute o$ the

entit&%


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(rimar& *e& is theattribute or combination

o$ attributes that

uni)uel& identi$ies a

s(eci$ic row in a table%


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In some tables. two or more attributes

ma& be 1oined to $orm the (rimar& *e&%


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DVIS2,S

d#isor No% Last Name First Name 2$$ice No%

1418 +o,ard len 420

1419 Melton Am. 316

1503 !an& i 202

1506 ado,si % 203

STUDENTS

Student ID Last NameFirst

Name Phone No%d#isor

No%

333-33-3333 Simpson Alice 333-3333 1418111-11-1111 Sanders Ned 444-4444 1418

123-45-6789 Moore Artie 555-5555 1503

$oreign *e& is an attribute in one table that is a (rimar& *e& in

another table%


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DVIS2,S


1418 +o,ard len 420

1419 Melton Am. 316

1503 !an& i 202

1506 ado,si % 203

Foreign *e&s are used to lin* tables together%

STUDENTS



No%


123-45-6789 Moore Artie 555-5555 1503


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DVIS2,S


1418 +o,ard len 420

1419 Melton Am. 316

1503 !an& i 202

1506 ado,si % 203

2ther non+*e& attributes in each table store im(ortant

in$ormation about the entit&%

STUDENTS



No%


123-45-6789 Moore Artie 555-5555 1503


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RELATIONAL DATAASES" ,lternati$es %or storing data

6ne possible alternate approach 'ould be to storeall data in one uni%orm table.

4or e#ample& instead o% separate tables %orstudents and classes& 'e could store all data in onetable and ha$e a separate line %or each student #class combination.


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Student IDLast

NameFirstName Phone No% 'ourse No% Section Da& Time

333-33-3333 Simpson Alice 333-3333 A$$*-3603 1 M 900 AM

333-33-3333 Simpson Alice 333-3333 N-3213 3 *! 1100 AM

333-33-3333 Simpson Alice 333-3333 MM*-3021 11 *! 1200 M

111-11-1111 Sanders Ned 444-4444 A$$*-3433 2 * 1000 AM

111-11-1111 Sanders Ned 444-4444 MM*-3021 5 800 AM

111-11-1111 Sanders Ned 444-4444 ANS-1422 7 900 AM

123-45-6789 Moore Artie 555-5555 A$$*-3433 2 * 1000 AM

123-45-6789 Moore Artie 555-5555 N-3213 3 *! 1100 AM

• :sing the suggested approach& a student ta;ing three classes 'ould

need three ro's in the table.

• -n the abo$e& simpli%ied e#ample& a number o% problems arise.


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Student IDLast





111-11-1111 Sanders Ned 444-4444 A$$*-3433 2 * 1000 AM

111-11-1111 Sanders Ned 444-4444 MM*-3021 5 800 AM


123-45-6789 Moore Artie 555-5555 A$$*-3433 2 * 1000 AM

123-45-6789 Moore Artie 555-5555 N-3213 3 *! 1100 AM

• *uppose ,lice *impson changes her phone number. Jou need to ma;e

the change in three places. -% you %ail to change it in all three places orchange it incorrectly in one place& then the records %or ,lice 'ill beinconsistent.

• /his problem is re%erred to as an update anomaly.


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Student IDLast





111-11-1111 Sanders Ned 444-4444 A$$*-3433 2 * 1000 AM

111-11-1111 Sanders Ned 444-4444 MM*-3021 5 800 AM


123-45-6789 Moore Artie 555-5555 A$$*-3433 2 * 1000 AM

123-45-6789 Moore Artie 555-5555 N-3213 3 *! 1100 AM

• =hat happens i% you ha$e a ne' student to add& but he hasnt signed up

%or any courses yetK

• 6r 'hat i% there is a ne' class to add& but there are no students enrolledin it yetK -n either case& the record 'ill be partially blan;.

• /his problem is re%erred to as an insert anomaly.


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Student IDLast





111-11-1111 Sanders Ned 444-4444 A$$*-3433 2 * 1000 AM

111-11-1111 Sanders Ned 444-4444 MM*-3021 5 800 AM


123-45-6789 Moore Artie 555-5555 A$$*-3433 2 * 1000 AM

123-45-6789 Moore Artie 555-5555 N-3213 3 *! 1100 AM

• -% ed 'ithdra's %rom all his classes and you eliminate all three o% his

ro's %rom the table& then you 'ill no longer ha$e a record o% ed. -% edis planning to ta;e classes ne#t semester& then you probably didntreally 'ant to delete all records o% him.

• /his problem is re%erred to as a delete anomaly.


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RELATIONAL DATAASES

" ,lternati$es %or storing data ,nother possible approach 'ould be to store each

student in one ro' o% the table and create multiple

columns to accommodate each class that he ista;ing.


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• /his approach is also %raught 'ith problems

– Go' many classes should you allo' in building the tableK

– /he abo$e table is


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• /he solution to the preceding problems is

to use a set o% tables in a relationaldatabase.

• Each entity is stored in a separate table&and separate tables or %oreign ;eys can beused to lin; the entities together.


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RELATIONAL DATAASES" !asic re#uirements of a relational database

E$ery column in a ro' must be single $alued. -n other 'ords& e$ery cell can ha$e one and only one $alue.

-n the student table& you couldnt ha$e an attributenamed Phone umber i% a student could ha$emultiple phone numbers.

/here might be an attribute named local phonenumber and an attribute named permanent phone

number. Jou could not ha$e an attribute named Class in the

student table& because a student could ta;e multipleclasses.


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RELATIONAL DATAASES

" !asic re#uirements of a relationaldatabase /he primary ;ey cannot be null.

/he primary ;ey uni


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• ote that 'ithin each table& there are noduplicate primary ;eys and no null primary;eys.

• Consistent 'ith the entity integrity rule.


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RELATIONAL DATAASES" !asic re#uirements of a relational

database , %oreign ;ey must either be null or correspond to

the $alue o% a primary ;ey in another table. /his rule is re%erred to as the referential

integrity rule.

/he rule is necessary because %oreign ;eys are usedto lin; ro's in one table to ro's in another table.


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DVIS2,S


1418 +o,ard len 420

1419 Melton Am. 316

1503 !an& i 202

1506 ado,si % 203

STUDENTS



No%


123-45-6789 Moore Artie 555-5555 1503

d#isor No% is a $oreign *e& in the STUDENTS table% E#er&

incident o$ d#isor No% in the STUDENTS table either matches

an instance o$ the (rimar& *e& in the DVIS2,S table or is null%


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RELATIONAL DATAASES" !asic re#uirements of a relational

database ,ll non!;ey attributes in a table should describe a

characteristic o% the ob8ect identi%ied by theprimary ;ey. Could nationality be a non!;ey attribute in the

student tableK

Could adisor!s nationality be a non!;eyattribute in the student tableK


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RELATIONAL DATAASES

" /he preceding %our constraints produce a 'ell!structured normali+ed database in 'hich Data are consistent.

Redundancy is minimi+ed and controlled.

" -n a normali+ed database& attributes appearmultiple times only 'hen they %unction as%oreign ;eys.

" /he re%erential integrity rule ensures there 'ill be no update anomaly problem 'ith %oreign;eys.


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RELATIONAL DATAASES

" ,n important %eature is that data about $arious things o%interest entities are stored in separate tables. )a;es it easier to add ne' data to the system.

Jou add a ne' student by adding a ro' to the student

table. Jou add a ne' course by adding a ro' to the course table. )eans you can add a student e$en i% he hasnt signed up

%or any courses. ,nd you can add a class e$en i% no students are yet

enrolled in it.

)a;es it easy to a$oid the insert anomaly." *pace is also used more e%%iciently than in the other

schemes. /here should be no blan; ro's or attributes.

• ,dd a


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studenthere.

• Lea$es no

blan;spaces.

• ,dd a course here.• Lea$es no blan; spaces.

• =hen a particular student enrolls %or aparticular course& add that in%o here.


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RELATIONAL DATAASES" Deletion o% a class %or a student 'ould cause the

elimination o% one record in the student # classtable.

/he student still e#ists in the student table. /he class still e#ists in the class table.

,$oids the delete anomaly.


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• ed stille#ists inthe student

table.

•E$en i% ed 'as the only student inthe class& ,CC/!3?03 still e#ists in thecourse table.

• -% ed *anders drops ,CC/!3?03& remo$eeds class %rom this table.


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Re&ati'na& Data Tab&es

!10


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Re&ati'na& Data Tab&es

!11

Primary Meys

$oreign %ey Customer N is a 4oreign ;ey inthe *ales /able because it is a Primary ;ey that uni


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Wh( )ave a Set '* Re&ate% Tab&es?

" Data stored in one large table can be redundantand ine%%icient causing the %ollo'ing problems :pdate anomaly

-nsert anomaly

Delete anomaly

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Re&ati'na& Database Design R+&es

" E$ery column in a ro' must be single $alued" Primary ;ey cannot be null empty also ;no'n as entity integrity

" -4 a %oreign ;ey is not null& it must ha$e a $alue that corresponds tothe $alue o% a primary ;ey in another table re%erential integrity

" ,ll other attributes in the table must describe characteristics o% the

ob8ect identi%ied by the primary ;ey

4ollo'ing these rules allo's databases to be normali+ed and sol$es theupdate& insert& and delete anomalies.

!13


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,e( Ter-s" Database

" Database management systemD()*

" Database system

" Database administrator D(,

" Data 'arehouse

" (usiness intelligence

" 6nline analytical processing6L,P

" Data mining

" Record layout

" Logical $ie'

" Physical $ie'

" *chema

" Conceptual!le$el schema

" E#ternal!le$el schema

" *ubschema" -nternal!le$el schema

" Data dictionary

" Data de%inition languageDDL

" Data manipulation languageD)L

" Data


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,e( Ter-s c'ntin+e%/" :pdate anomaly

" -nsert anomaly

" Delete anomaly

" Relational database

" Entity integrity rule

" Re%erential integrity rule

" ormali+ation

" *emantic data modeling

Documents

AIS relational databases