1111

Introduction to Entities, Attributes, and Relationships

Introduction to Entities, Attributes, and Relationships

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OverviewOverview

• Why conceptual modeling?

• Introduction of the Key role players:

– Entities

– Attributes

– Relationships

• Why conceptual modeling?

• Introduction of the Key role players:

– Entities

– Attributes

– Relationships

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Why Create a Conceptual Model?Why Create a Conceptual Model?

• It describes exactly the information needs of the It describes exactly the information needs of the businessbusiness

• It facilitates discussionIt facilitates discussion

• It helps to prevent mistakes, misunderstandingIt helps to prevent mistakes, misunderstanding

• It forms important “ideal system” documentationIt forms important “ideal system” documentation

• It forms a sound basis for physical database It forms a sound basis for physical database designdesign

• It is a very good practice with many practitionersIt is a very good practice with many practitioners

• It describes exactly the information needs of the It describes exactly the information needs of the businessbusiness

• It facilitates discussionIt facilitates discussion

• It helps to prevent mistakes, misunderstandingIt helps to prevent mistakes, misunderstanding

• It forms important “ideal system” documentationIt forms important “ideal system” documentation

• It forms a sound basis for physical database It forms a sound basis for physical database designdesign

• It is a very good practice with many practitionersIt is a very good practice with many practitioners

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Between Dream and Reality...Between Dream and Reality...

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Entity Relationship ModelingEntity Relationship Modeling

• Models business,not implementation

• Is a well-established technique

• Has a robust syntax

• Results in easy-to-read diagrams…

...although they maylook rather complex at first sight

• Models business,not implementation

• Is a well-established technique

• Has a robust syntax

• Results in easy-to-read diagrams…

...although they maylook rather complex at first sight

SUPPLIER# SUPPLIER CODEo EMAIL* APPROVED* REFERENCE

OTHER ORGANIZATION

ORGANIZATIONo EMAIL* NAMEo POSTAL CODEo REGIONo STREETo TOWNo TELEPHONE NUMBERo CONTACT NAMEo CONTACT EXTENSION

MEMBERSHIP TYPE# CODE* DESCRIPTION* DISCOUNT PERCENTAGEo STANDARD FEE

MEMBERSHIP PERIOD# START DATEo ACTUAL FEE PAID

MEMBERSHIP# NUMBERo TERMINATION REASONo TERMINATION DATE

EMPLOYEE* POSITION* LAST NAMEo FIRST NAMEo OTHER INITIALSo EMAIL

BOOKING* BOOK DATEo EXPIRE DATEo NOTIFY DATEo RESERVE DATEo STAFF REMARKS

RENTAL ITEM# LINE NO* RENTAL PERIOD* PRICE PAIDo RETURN DATEo STAFF REMARKS

RENTAL* RENTAL DATEo STAFF REMARKSo COMPLETED

COPY* ACQUIRE DATE* PURCHASE COST* SHELF CODEo CONDITIONo CUSTOMER REMARKS...

REVIEW# SEQUENCE* ARTICLE* HOTo AUTHORo URL

PUBLICATION# REFERENCE* TITLEo VOLUMEo ISSUEo PUBLISH DATE

CUSTOMERo EMAIL* DESIGNATION* FIRST NAME* LAST NAMEo OTHER INITIALS* STREET* TOWN* POSTAL CODE* REGIONo HOME PHONEo WORK EXTENSIONo WORK PHONEo PHOTOGRAPHo STAFF REMARKS

CATALOG# REFERENCEo CATALOG DATEo DESCRIPTION

MOVIE* CATEGORYo AGE RATING* DURATION* MONOCHROMEo AUDIOo PREVIEW

GAME* CATEGORY* MEDIUMo MINIMUM MEMORY

TITLE# PRODUCT CODE* TITLEo DESCRIPTION

PRICE LEVEL# CODE* DESCRIPTION

PRICE HISTORY# EFFECTIVE DATE* PRICE* DEFAULT DAYS* OVERDUE RATE

for

used for

of

renewed for

of

the type of

held by

the holder of

held by

the holder of

availablefrom

thedistributor for

requestedagainst the

requestorof

authorized by

responsiblefor

the reservation for

reserved on

for

on

cancelled by

the cancellor of

approved by

responsible for

of

reviewed in

at

applied to

the rental for

fulfilled as

part of

composed of

for

rented on

approved by

responsiblefor

part of

parent organization of

acquired from

the source of

of

available as

for

defined by

managed by

the manager of

in

the source of

in

the source of

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Goals of Entity Relationship ModelingGoals of Entity Relationship Modeling

• Capture all required information

• Information appears only once

• Model no information that is derivable from other information already modeled

• Information is in a predictable, logical place

• Capture all required information

• Information appears only once

• Model no information that is derivable from other information already modeled

• Information is in a predictable, logical place

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Database TypesDatabase Types

HierarchicalHierarchical

RelationalRelational

NetworkNetwork

ER ModelER Model

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EntityEntity

• An Entity is:

– “Something” of significance to the business about which data must be known.

– A name for the things that you can list.

– Usually a noun.

• Examples: objects, events

• Entities have instances.

• An Entity is:

– “Something” of significance to the business about which data must be known.

– A name for the things that you can list.

– Usually a noun.

• Examples: objects, events

• Entities have instances.

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Entities and InstancesEntities and Instances

PERSON

PRODUCT

PRODUCT TYPE

EMPLOYMENT CONTRACT

JOB

SKILL LEVEL

TICKET RESERVATION

PURCHASE

ELECTION

PRINTER PREFERENCE

DOCUMENT VERSION

PERSON

PRODUCT

PRODUCT TYPE

EMPLOYMENT CONTRACT

JOB

SKILL LEVEL

TICKET RESERVATION

PURCHASE

ELECTION

PRINTER PREFERENCE

DOCUMENT VERSION

Mahatma Gandhi

2.5 x 35 mm copper nail

nail

my previous contract

violinist

fluent

tonight: Hamlet in the Royal

the CD I bought yesterday

for parliament next fall

…

...

Mahatma Gandhi

2.5 x 35 mm copper nail

nail

my previous contract

violinist

fluent

tonight: Hamlet in the Royal

the CD I bought yesterday

for parliament next fall

…

...

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Entities and SetsEntities and Sets

dish washerdish washer

JOB

waiterwaiter

cookcookwaitresswaitress

managermanager

financial controllerfinancial controller

porterporter

piano playerpiano player

• An entity represents a set of instances that are of interest to a particular business.

• An entity represents a set of instances that are of interest to a particular business.

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AttributeAttribute

• Also represents something of significance to the business

• Is a single valued property detail of an entity

• Is a specific piece of information that:

– Describes

– Quantifies

– Qualifies

– Classifies

– Specifies

an entity.

• Also represents something of significance to the business

• Is a single valued property detail of an entity

• Is a specific piece of information that:

– Describes

– Quantifies

– Qualifies

– Classifies

– Specifies

an entity.

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Attribute ExamplesAttribute Examples

Entity

EMPLOYEE

CAR

ORDER

JOB

TRANSACTION

EMPLOYMENT CONTRACT

Entity

EMPLOYEE

CAR

ORDER

JOB

TRANSACTION

EMPLOYMENT CONTRACT

Attribute

Family Name, Age, Shoe Size,

Town of Residence, Email, ...

Model, Weight, Catalog Price, …

Order Date, Ship Date, …

Title, Description, ...

Amount, Transaction Date, …

Start Date, Salary, ...

Attribute

Family Name, Age, Shoe Size,

Town of Residence, Email, ...

Model, Weight, Catalog Price, …

Order Date, Ship Date, …

Title, Description, ...

Amount, Transaction Date, …

Start Date, Salary, ...

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RelationshipsRelationships

• Also represent something of significance to the business

• Express how entities are mutually related

• Always exist between two entities (or one entity twice)

• Always have two perspectives

• Are named at both ends

• Also represent something of significance to the business

• Express how entities are mutually related

• Always exist between two entities (or one entity twice)

• Always have two perspectives

• Are named at both ends

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Relationship ExamplesRelationship Examples

EMPLOYEES have JOBS

JOBS are held by EMPLOYEES

EMPLOYEES have JOBS

JOBS are held by EMPLOYEES

PRODUCTS are classified by a PRODUCT TYPE

PRODUCT TYPE is a classification for a PRODUCT

PRODUCTS are classified by a PRODUCT TYPE

PRODUCT TYPE is a classification for a PRODUCT

PEOPLE make TICKET RESERVATIONS

TICKET RESERVATIONS are made by PEOPLE

PEOPLE make TICKET RESERVATIONS

TICKET RESERVATIONS are made by PEOPLE

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JOB

waiterwaiter

cookcookwaitresswaitress

managermanager

financial controllerfinancial controller

porterporter

piano playerpiano player

Employees have JobsEmployees have Jobs

AhmedAhmed

JillJillAdamAdam

MariaMaria

EMPLOYEEEMPLOYEE

Numerical observation:

• All EMPLOYEES have a JOB

• No EMPLOYEE has more than one JOB

• Not all JOBS are held by an EMPLOYEE

• Some JOBS are held by more than one EMPLOYEE

Numerical observation:

• All EMPLOYEES have a JOB

• No EMPLOYEE has more than one JOB

• Not all JOBS are held by an EMPLOYEE

• Some JOBS are held by more than one EMPLOYEE

ShintaroShintaro dish washerdish washer

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Entity Representation in DiagramEntity Representation in Diagram

• Drawn as a “softbox”

• Name singular

• Name inside

• Neither size, nor position has a special meaning

• Drawn as a “softbox”

• Name singular

• Name inside

• Neither size, nor position has a special meaning

EMPLOYEE

TICKETRESERVATION

JOB ASSIGNMENT

JOB

ORDERE

LEC

TIO

N

During design, entities usually lead to tables.

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Attributes in DiagramsAttributes in Diagrams

*o

EMPLOYEE Family Name Addresso Birth Dateo Shoe Sizeo Email

JOB Titleo Description

During design, attributes lead to columns.

*

*

*

Mandatory attribute, that is, known and available for every instance

Optional attribute, that is, unknown or unimportant to know for some instances

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Jobs are held by one or more employees

An employee has exactly one jobAn employee has exactly one jobhas

Relationship in DiagramsRelationship in Diagrams

EMPLOYEE JOB has

held by

held by

exactly one

one or more

During design, relationships lead to foreign keys.

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EMPLOYEE JOB

Two PerspectivesTwo Perspectives

hashas

held byheld by

mandatory:mandatory:mandatory:mandatory: optional:optional:optional:optional:

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Every EMPLOYEE has exactly one JOB

One WayOne Way

hashasEMPLOYEE JOB

held byheld by

mandatory:mandatory:mandatory:mandatory: optional:optional:optional:optional:

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The Other WayThe Other Way

hashasEMPLOYEE JOB

held byheld by

mandatory:mandatory:mandatory:mandatory: optional:optional:optional:optional:

A JOB may be held by one or more EMPLOYEES

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””““EachEach PP split intosplit intomust bemust be

may bemay be one or more Qsone or more Qsexactly one Qexactly one Q““EachEach P P may be may be split intosplit into one or more one or more Qs Qs””

““EachEach QQ part ofpart of ””must bemust be

may bemay be one or more Psone or more Psexactly one Pexactly one P““EachEach Q Q must be must be part of part of exactly oneexactly one P P””

Reading a Relationship EndReading a Relationship End

P split intosplit into Qpart ofpart of

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Functions Drive DataFunctions Drive Data

• Business functions are always present.

– Explicit

– Assumed

• Business functions need data.

• An entity, attribute, or relationship may be modeled because:

– It is used by a business function.

– The business need may arise in the near future.

• Business functions are always present.

– Explicit

– Assumed

• Business functions need data.

• An entity, attribute, or relationship may be modeled because:

– It is used by a business function.

– The business need may arise in the near future.

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Weather ForecastWeather Forecast

KøbenhavnBremenBerlinMünchenAmsterda

mBruxellesParisBordeaux

1/-5

7/2

3/-1

8/3

5/-3

4/0

4/1

0/-3

January 263

3

3

4

3

2

3

4

****

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(Copenhagen)

Bremen

Berlin

(Munich)

Bruxelles

Paris

Bordeaux

Amsterdam

UKUK

FRFR

DEDE

DKDK

CHCH

NLNL

BEBE

ITIT

LULU

IRIR

København

München

(Brussels)

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located in

having

referring to

referred in

about

Weather Forecast, a Solution Weather Forecast, a Solution

WEATHER TYPE* Icon* Description

WIND DIRECTION* Icon* Description

COUNTRY* Nameo Geographical Position

CITY* Nameo Geographical Position

FORECAST* Dateo Minimum Temperatureo Maximum Temperatureo Wind Force

referring to

referred in

subject of

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Graphical Elements of ER DiagramGraphical Elements of ER Diagram

SubtypeSubtype

##

Unique identifierUnique identifier

ArcArcArcArc

NontransferabilityNontransferabilityNontransferabilityNontransferability

** **o

o

EntityEntity

AttributeAttribute

RelationshipRelationship

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SummarySummary

• ER Modeling models information conceptually

• Based on functional business needs

• “What”, not “How”

• Diagrams provide easy means of communication

• Detailed, but not too much

• ER Modeling models information conceptually

• Based on functional business needs

• “What”, not “How”

• Diagrams provide easy means of communication

• Detailed, but not too much

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PracticesPractices

• Instance or Entity

• Guest

• Reading

• Hotel

• Recipe

• Instance or Entity

• Guest

• Reading

• Hotel

• Recipe

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Practice: Instance or Entity?Practice: Instance or Entity?

PRESIDENT

ELLA FITZGERALD

DOG

ANIMAL

HEIGHT

E CAR

A CAR

I CAR

Concept E/A/I? Example Instance or EntityConcept E/A/I? Example Instance or Entity

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Practice: GuestPractice: Guest

GUESTGUEST

HOTELHOTEL

ROOMROOM

AddressAddress

Arrival Date Arrival Date

Family NameFamily Name

Room NumberRoom Number

Floor NumberFloor Number

Number of BedsNumber of Beds

Number of Parking Lots Number of Parking Lots

PricePrice

TV set available?TV set available?

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Practice: ReadingPractice: Reading

Each EMPLOYEE may be assigned to one or more DEPARTMENTS

Each DEPARTMENT must be responsible for one or more EMPLOYEES

Each EMPLOYEE must be assigned to one or more DEPARTMENTS

Each DEPARTMENT may be responsible for one or more EMPLOYEES

Each EMPLOYEE must be assigned to exactly one DEPARTMENT

Each DEPARTMENT may be responsible for exactly one EMPLOYEE

Each EMPLOYEE may be assigned to one or more DEPARTMENTS

Each DEPARTMENT must be responsible for one or more EMPLOYEES

Each EMPLOYEE must be assigned to one or more DEPARTMENTS

Each DEPARTMENT may be responsible for one or more EMPLOYEES

Each EMPLOYEE must be assigned to exactly one DEPARTMENT

Each DEPARTMENT may be responsible for exactly one EMPLOYEE

EMPLOYEEEMPLOYEE DEPARTMENTDEPARTMENTassigned toassigned to

responsible forresponsible for

AA

BB

CC

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Practice: Read and CommentPractice: Read and Comment

TOWNTOWN

birthplace ofbirthplace of

born inborn in

living inliving in

home town ofhome town of

mayor ofmayor of

with mayorwith mayor

PERSONPERSON

visitor ofvisitor of

visited byvisited by

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Practice: HotelPractice: Hotel

HOTEL* Address

STAY* Arrival Date

ROOM* Room Number

PERSON* Name

inin

the lodging the lodging forfor

ofof

withwith

inin

withwith

guest inguest in

host ofhost of

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Açorda alentejanabread soup from Portugal

Ralph’s Raving Recipes

Cut the onion into small pieces and fry together with the garlic. Wash the red pepper, cut it in half, remove the seeds and fry it for at least 15

page 127

preparation

vegetarian15 mineasy

1 onion4 cloves of garlic1 red pepper1 liter of vegetable broth4 tablespoons of olive oil4 fresh eggs1 handful of parsley or coriandersalt, pepper9-12 slices of (old) bread

for 4 persons:

Soups