D b dDatabase: Introduction

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Database SystemsDatabase SystemsImportant topic in the study of information systemsinformation systems

Store/track items: scalar data (names, dates, …), pictures, audio, videoE l l l Early applications: internal usesInternet: publishing database content to users

Database design and developmentDatabase design and developmentUnderstand, gather and organize user requirementsqTransform the designs into physical databases (applications)

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What is a Database System?What is a Database System?An electronic filing cabinetA ll ti f d t hi h iA collection of data which is:

IntegratedCollect/unify data from a number of different Collect/unify data from a number of different sources

SharedAccess by more than one person/application

Advantages:Data is shared, redundancy can be reduced, and integrity maintained

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Description of System

requirements

Dataanalysis

ER Data modelanalysis model

Data LogicalLook for entities Data

designLogical

Data modelentities, relationships and attributes

C ER

Physical D t d l

PhysicalDatabase

Convert ER model (with cardinalities) i t t bl Data modelb se

designinto table definitions

Choose appropriate

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pp pcolumn types and constraints

El m ts f E tit R l ti ship Elements of Entity-Relationship ModelModel

Entities, attributes, identifiers, and relationshipsrelationshipsEntity:

Thing or object, whether real or imagined, Thing or object, whether real or imagined, about which information needs to be known/trackedExample:Example:

A customer called Peter Lam is an entityEntity can be

Weak entity: existence-dependent on other entitiesParent and child

Strong entity: non-dependent on other entities

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g y p

El m ts f E tit R l ti ship Elements of Entity-Relationship Model: EntityModel Entity

Entity class/type:A collection that share

CUSTOMER entity class t iA collection that share

common properties or characteristics

contains:CustIDFirstName

UPPER CASE (noun)Entity instance:

R f

FirstNameLastNamephoneNo

Representation of a particular entity

Many instances in an Two instances:

Many instances in an entity class 1 Peter Lam 2134

2 Jenny Chan 1234

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El m ts f E tit R l ti ship Elements of Entity-Relationship Model: AttributesModel Attributes

Attributes:Properties

attributeValue of theProperties

describe the entity’s characteristicsValue of the attribute “phoneNo”

CustID FirstName LastName phoneNoCustID FirstName LastName phoneNo

1 Peter Lam 2134

2 Jenny Chan 1234

7An entity instance

Elements of Entity-Relationship f y pModel: Relationships

D ib h titi Describes how one or more entities are related to each otherEntity: noun, relationship: verb

places

ER Diagram

CUSTOMER ORDERp

attendsBinary

RelationshipsSTUDENT SUBJECT

attendsRelationships(degree 2)

GRADEEXAM determines

Degree 3 relationships

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CONTASSrelationships

T p s f Bi R l ti shipTypes of Binary RelationshipOne to one (1:1)One-to-one (1:1)One to many (1:N)yMany to many (N:M)

i i dPROJECT STUDENT1:1

is_assigned_to

GROUP PROJECT STUDENT1:Nis_assigned_to

SUBJECT STUDENTN:M

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enrolled

R l ti hiRelationshipMaximum cardinality:Maximum cardinality:

The maximum number of entities that can id f th l ti hioccur on one side of the relationship

1:N, if a group project involves at most 3 st d tsstudents

Maximum cardinality: 1:3Mi i di litMinimum cardinality:

Indicates whether participation in the l h d lrelationship is mandatory or optional

0: optional, 1: mandatory

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Relationshipi i d t

PROJECT STUDENT1:1is_assigned_to1 0

entity optional Relationship Number entityinvolved

O j t M b A i d t O St d tOne project May be Assigned to One Student

One Student Must be Assigned one project

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RelationshipRelationship

GROUP PROJECT STUDENT1 Nis_assigned_to1 0GROUP PROJECT STUDENT1:N1 0

entity optional Relationship Number i l d

entityinvolved

Group Studentproject

St d t

Student

j tStudent project

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RelationshipSUBJECT STUDENTN:M1 1

enrolled

entity optional Relationship Number entityy p pinvolved

y

subject Student

Student subject

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Attributes?

Example 1Example 1Project:

P j t titl (P jTitl ) P j t ID (P jID) d Project title (ProjTitle), Project ID (ProjID) and Budget (ProjBudget)

Student:Student:Year of study (YearStudy), Student Number (StudNo), First Name (FirstName) and Last Name ( ), m ( m ) m(LastName)

Relationship:pA project might be assigned to one studentA student must be assigned one project

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Example 2Example 2An order must contain at least one product.A product might not associate with any orderAn order

consists of an order number as well as an order dateThe product name and its description will be listed outAlso, the quantity of a particular product will be listed as well.

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Example 3Example 3A subject must have at least one student

ll denrolledA student must enroll at least one subjectA subject has a title as well as a subject code A student has a student number, first name and last nameand last nameThe enrollment date should be recorded

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Binary RelationshipsEntitles tables

Subject tablejTwo columns: subcode, title

One to one binary relationshipOne-to-one binary relationshipPrimary key on one side (mandatory side) b f i k th th id becomes a foreign key on the other side (optional side)

Both mandatory: place on one side onlyOne side mandatory, one side optional: place on

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optional side

Rule 1D i 1 Rule 1is_assigned_to

Design 1

PROJECT STUDENT1:1

PROJECT ProjID title name

STUDENT studNo ProjID firstName lastName

Go from Student to Project dN b d ’ DENuse studNo to obtain a student’s row in STUDENT

obtain ProjID assigned to studNouse this ProjID to look up the data in PROJECT

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use this ProjID to look up the data in PROJECT

Rule 1D i 2 Rule 1is_assigned_to

Design 2

PROJECT STUDENT1:1

PROJECT ProjID title name studNo

STUDENT studNo firstName lastName

Go from Project to Studentuse projID to obtain a project’s row in PROJECTobtain studNo assigned to projIDuse this studNo to look up the student info in STUDENT

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use this studNo to look up the student info in STUDENT

Rule 1Rule 1Both side mandatory:

One project must assign to one studentOne student must be assigned one projectDesign 1 and design 2 are conceptually the sameDesign 1 and design 2 are conceptually the same

Might be different in performanceQuery in one direction is more common than query in th th di tithe other direction

One side mandatory, one side optional?A student must be assigned one projectA student must be assigned one projectA particular project may not be assigned to any student

l k kDesign 1: looks okDesign 2: null value

Design 1 is preferable

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Design 1 is preferable

Rule 2Rule 2One-to-many binary relationship

Key on parent: placed in childCf: one-to-one relationshipp

GROUP PROJECT STUDENT1is_assigned_to1 0GROUP PROJECT STUDENT1:N1 0

GROUP PROJECT

ProjID title namePROJECT

STUDENT studNo ProjID firstName lastName

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STUDENT studNo ProjID firstName lastName

Rule 3many-to-many binary relationship

Cannot be directly represented by relations as one-to-one or one-to-many casesReason

B E { b d }SUBJECT entity: {subCode, name}STUDENT entity: {studNo, firstName, lastName}lastName}Multiple values for Many-to-many relationship!

SUBJECT STUDENTN:M

enrolled

1 1

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Rule 3many-to-many binary relationship

Create a new relation with primary keys of the two entities as its primary keyp y yIntersection relations

SUBJECT Subcode name

STUDENT studNo firstName lastName

SUBJECTSUBJECT-STUDENT studNo SubID

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Many to Many RelationshipMany-to-Many RelationshipAssociative entities:Associative entities:

title studNoenrolledtitle

SUBJECT STUDENTN:M

enrolled

1 1

codedateEnrolled firstName

lastNamedateEnrolled

SUBJECT code title Natural?

STUDENT studNo firstName lastName

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SUBJECT-STUDENT studNo code dateEnrolled

Many to Many RelationshipMany-to-Many RelationshipAssociative entities:Associative entities:

SUBJECT code title

STUDENT studNo firstName lastName

SUBJECT-STUDENT studNo code dateEnrolledrefNoSUBJECT-STUDENT studNo code dateEnrolledrefNo

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Many-to-Many Relationshipy y pOrder: unique orderID and dateProducts: prodID name descriptionProducts: prodID, name, descriptionEach order can include more than one product

containsorderID

prodIDprodName

ORDER PRODUCTM:Ncontains

0 1

prodDesorderDate qty

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Ternary RelationshipsCUSTOMER, SALESPERSON, ORDER

Each order involves one and only one Each order involves one and only one customerA customer can have many ordersA customer can have many ordersOne order has one and only one salesA sales has many ordersA sales has many orders

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Ternary RelationshipTernary RelationshipFurther constraint?

Each customer can place orders only with a particular salespersonp pBusiness rule

Need to be documentedNeed to be documented

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“Relational” TerminologiesP im KPrimary Key

An attribute (or combination or attributes) that uniquely identifies a row in a relationuniquely identifies a row in a relation

Candidate KeyAttribute that can be chosen to be the primary k

p ykey

Composite KeyA im k th t sists f m th A primary key that consists of more than one attribute

Foreign KeyForeign KeyAn attribute in a relation that serves as the primary key of another relation

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NormalizationNormalizationProcess for evaluating and converting a Process for evaluating and converting a relation to reduce modification n m li s ( nd si bl ns n f anomalies (undesirable consequence of

a data modification) d l d d dDetects and eliminates data redundancy

Well structure relations should avoidInsertion anomalyDeletion anomalyDeletion anomalyModification anomaly

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Example for Normal FormspProject Assignment:

One project: assigned to a no of deptsOne project: assigned to a no of deptsUnnormalized form: all information together

ProjID Title DeptNo DeptName Locaton NoStaff HourChg ExChg Hours

123 A 12 Engineering China 5 100 20 10

123 A 40 HRO HK 6 50 0 4123 A 40 HRO HK 6 50 0 4

123 A 70 Finance HK 2 80 0 4

234 B 12 Engineering China 3 100 20 60

234 B 70 Finance HK 1 80 0 7

345 C 14 Purchase Taiwan 3 50 40 6

456 D 70 Finance HK 1 80 0 5456 D 70 Finance HK 1 80 0 5

567 E 12 Engineering China 10 100 20 30

567 E 70 Finance HK 1 80 0 18

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577 F 58 Sales China 20 60 20 20

First Normal FormFirst Normal Form1NF:

A relation must have only single-valued attributes

No repeating groupsPROJECT entity:JE y

ProjID, DeptNoTitle, DeptName, Location, NoStaff, pHourChg, ExChg, Hours

May have modification anomaliesA new dept added? Delete ProjID 577?

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1NFProjID DeptNo Title DeptName Locaton NoStaff HourChg ExChg Hours

123 12 A Engineering China 5 100 20 10

123 40 A HRO HK 6 50 0 4

123 70 A Finance HK 2 80 0 4123 70 A Finance HK 2 80 0 4

234 12 B Engineering China 3 100 20 60

234 70 B Finance HK 1 80 0 7

345 14 C Purchase Taiwan 3 50 40 6

456 70 D Finance HK 1 80 0 5

567 12 E Engineering China 10 100 20 30567 12 E Engineering China 10 100 20 30

567 70 E Finance HK 1 80 0 18

577 58 F Sales China 20 60 20 20

K : {P jID D tN }

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Key: {ProjID, DeptNo}

Second Normal FormSecond Normal Form2NF: 2NF

A relation must be in 1 NF and each non-key attribute must be dependent on the key attribute must be dependent on the whole key

T d t hi h i f ti ll To remove data which is functionally dependent upon only part of a key andTo place this data to a new relation, with that part of the key as the with that part of the key as the primary key

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Second Normal FormSecond Normal FormPROJECT entity:

Key: {ProjID, DeptNo}Title, DeptName, Location, NoStaffInv, HourChg, p gExChg, Hours

Dependency:p yProjID Title DeptNo DeptName, Location, HourChg, ExChgD p D p m , , g, E g{ProjID, DeptNo} NoStaffInv, Hours

Split up Relations

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Split up Relations

Second Normal Form: AnswerPROJECT entity:

ProjID, TitleProjID, TitleDEPT entity

DeptNo DeptName Location HourChg ExChgDeptNo, DeptName, Location, HourChg, ExChgASSINMENT entity

P jID D tN N St ffI HProjID, DeptNo, NoStaffInv, Hours

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2NFASSINMENT entityProjID Title

123 A

234 B

PROJECT entityProjID DeptNo NoStaff Hours123 12 5 10123 40 6 4 234 B

345 C

456 D

123 70 2 4234 12 3 60234 70 1 7 456 D

567 E

577 F

234 70 1 7345 14 3 6456 70 1 5

DeptNo DeptName Locaton HourChg ExChg

577 F567 12 10 30567 70 1 18577 58 20 20 DeptNo DeptName Locaton HourChg ExChg

12 Engineering China 100 20

40 HRO HK 50 070 Finance HK 80 014 Purchase Taiwan 50 40

58 Sales China 60 20

DEPT entity

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58 Sales China 60 20

Second Normal FormProblem:

ExChg depends on LocationExChg depends on LocationIf Location= HK, no ExChgIf L ti Chi E Ch 20If Location= China, ExChg = 20If Location = Taiwan, ExChg = 40

E lExample:Delete deptNo=14, deletion anomaly

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Third N rmal F rmThird Normal Form

3NF:A relation must be in 2 NF and no m Ftransitive dependencies may exist

A functional dependency between two or more A functional dependency between two or more non-key attributesDeptNo Location, ExChgp , gLocation ExChg

ExChg depends on non-key attribute “Location”Solution: split relation

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Third Normal Form: AnswerThird Normal Form AnswerPROJECT entity:

ProjID, TitleDEPT entity

DeptNo, DeptName, Location, HourChgEXTRACHARGE entity:y

Location, ExChgASSINMENT entityASSINMENT entity

ProjID, DeptNo, NoStaffInv, Hours

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3NFASSINMENT entityPROJECT entity

ProjID Title

123 A

PROJECT entityProjID DeptNo NoStaff Hours123 12 5 10123 40 6 4

EXTRACHARGE entity234 B

345 C

123 70 2 4234 12 3 60234 70 1 7

Location ExChg

China 20

456 D

567 E

234 70 1 7345 14 3 6456 70 1 5

HK 0

Taiwan 40

DeptNo DeptName Locaton HourChg

577 F567 12 10 30567 70 1 18577 58 20 20 DeptNo DeptName Locaton HourChg

12 Engineering China 100

40 HRO HK 5070 Finance HK 8014 Purchase Taiwan 50

58 Sales China 60

DEPT entity

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58 Sales China 60

Normalization vs D li tiDenormalization

Normalization:Normalization:Avoid modification anomaliesS li l iSplit relations

Extra processingMight not be desirable Denormalization: control data redundancy to

fimprove performance

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ExampleExampleAssume one HoD, one to three Deputy Assume one HoD, one to three Deputy HoDU /D li d l ti 1Un/De-normalized relation 1:

DEPT (DeptName, HOD, DeputyHoD)

Not in ________:D tN H D

Key: {DeptName, DeptyHoD}

DeptName HoDNormalized

DEPT (DeptName, HOD)DepHOD (DeptName DeputyHOD)

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DepHOD (DeptName, DeputyHOD)

ExampleExampleIn 2NF:

Not efficient: obtain data about dept, need to read at least 2 rows and as many as 4 rowsy

AlternativeDEPT (DeptName, HOD, DeHOD1, DeHOD2, DeHOD3)Key: DeptName

In __________All attributes are functionally dependent on All attributes are functionally dependent on DeptNameProblem: search the name of the DeHoD

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Problem search the name of the DeHoD

SQLSQL

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DBMSDBMSAccess:

Microsoft productWindows platformEasy to use: user-interfaceSmall companies, personal uses

M QL MySQL server:www.mysql.comPopular: available for windows, Linux, UnixM ltiMultiuserMultithread:

Enable database to perform multiple tasks concurrentlyIncrease server efficiency in handling client requestIncrease server efficiency in handling client request

Can handle large databases (tens of thousands of tables)(nearly) open source

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Graphical mode

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Graphical mode

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MySQLMySQL

Output format: table formC i i iCase insensitiveSemi-colon: line ends

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Data Definition LanguageData Definition Languagemysql> create database ABCpharmacy

>Create

->-> ;

Query OK 1 row affected (0.00 sec)databaseCreate Query OK, 1 row affected (0.00 sec)

mysql> use ABCpharmacy

Create tables

Database changedmysql> show tables;Empty set (0 00 sec)Empty set (0.00 sec)

mysql>

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mysqlDROP DATABASE db_name;

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Data Definition LanguageData Definition LanguageCreate tables

C t t bl t bl N m (DEFINITION)Create table tableName (DEFINITION)DEFINITION:

Col_name type [NOT NULL | NULL] [PRIMARY KEY]INT: integerDOUBLE: floating-point numberDECIMAL [M,D]: stores the digits in bytes: M: max display size, D: [ , ] g y p y ,max decimalsChar(M): fixed string: always occupying M bytesVARCHAR(M): variable length occupying at most M+1 bytes( ) g py g yENUM (‘val1’, ‘val2’, …) a string taken from a fixed set of values

Color ENUM (‘red’, ‘orange’, ‘yellow’, ‘green’, ‘blue’, ‘purple’)DESCRIBE tableName

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mDROP TABLE tableName

DDL Text File

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Data Definition LanguageData Definition Language

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The text file must be tab-delimited

Foreign key?Foreign key?Alter table table1Name ADD FOREIGN KEY (columnName) REFERENCES table2Name(columnName)E gE.g.,

Alter table orderInfo add foreign key ( ) f ( )(custName) references customer (name);

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Data Manipulation LanguageData Manipulation LanguageDML commands:

Querying DB: SELECTSQL: querying tablesSQL: querying tables

Statements written in multiple linesR d d l lReserved words: in capital letters

Conventions: provide clarityDo not required by compilers

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SELECT statement: retrievalSELECT statement retrievalSELECT <list of column expressions>FROM <list of tables and join operations>WHERE <list of logical expressions for rows>WHERE <list of logical expressions for rows>GROUP BY <list of grouping columns>HAVING <list of logical expressions for groups>HAVING <list of logical expressions for groups>ORDER BY <list of sorting specifications>

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SummarySummaryRevision

ER diagramTable designTable designNormalizationD n m li ti nDenormalizationSQL

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