Example BigHit Video Inc. wants to create an information system for online sales of movies in both DVD and videotape format. People will be allowed to.

ExampleExample

BigHit Video Inc. wants to create an information system for online BigHit Video Inc. wants to create an information system for online sales of movies sales of movies in both DVD and videotape formatin both DVD and videotape format. People will be . People will be allowed to register as customers of the online site and to update allowed to register as customers of the online site and to update their stored information. Information must be maintained about their stored information. Information must be maintained about customers’ shipping addresses, e-mail addresses and credit cards. customers’ shipping addresses, e-mail addresses and credit cards. In a single sale, customers will be allowed to purchase any quantity In a single sale, customers will be allowed to purchase any quantity of videos. The items in a single sale will be shipped to a single of videos. The items in a single sale will be shipped to a single address and will have a single credit card charge.address and will have a single credit card charge.A customer will be provided with a virtual shopping cart to store A customer will be provided with a virtual shopping cart to store items to be purchased. As each item is selected, it is added to the items to be purchased. As each item is selected, it is added to the shopping cart. When the customer finishes shopping, he will be shopping cart. When the customer finishes shopping, he will be directed to a checkout area where payment and shipping directed to a checkout area where payment and shipping information is entered. Once the sale is complete, the customer will information is entered. Once the sale is complete, the customer will be sent a receipt by e-mail.be sent a receipt by e-mail.

ExampleExample

Entities:Entities:Customer (key: account , last name, first Customer (key: account , last name, first name, address, email, credit card, name, address, email, credit card, password)password)

Movie (key: id, title, genre, length)Movie (key: id, title, genre, length)

Sale (key: id, cost, date, credit card)Sale (key: id, cost, date, credit card)Shopping Cart (key: id, date)Shopping Cart (key: id, date)

ExampleExample

Relationship Relationship TypeType

Entity ClassEntity Class Entity ClassEntity Class Cardinality Cardinality RatioRatio

AttibutesAttibutes

PurchasesPurchases CustomerCustomer SaleSale one-to-one-to-manymany

IncludesIncludes SaleSale MovieMovie many-to-many-to-manymany

quantityquantity

SelectsSelects CustomerCustomer ShoppingCaShoppingCartrt

one-to-one-to-manymany

IncludesIncludes ShoppingCShoppingCartart

MovieMovie many-to-many-to-manymany

quantityquantity

Data Modeling with E-R DiagramData Modeling with E-R Diagram

An An Entity-RelationshipEntity-Relationship (E-R) model is a (E-R) model is a high-level conceptual modelhigh-level conceptual model

E-R models are best described using E-R models are best described using graphical diagramsgraphical diagrams

This model provides designers with an This model provides designers with an accurate and useful model that avoids accurate and useful model that avoids confusion and is understandable by usersconfusion and is understandable by users

E-R modelE-R model

An An E-R modelE-R model includes includes– Entity classesEntity classes– Attributes of each classAttributes of each class– Relationship types between classesRelationship types between classes– ConstraintsConstraints

Types of attributesTypes of attributesDesignation of key attributesDesignation of key attributesCardinalities of relationship typesCardinalities of relationship types

An E-R Model is typically represented An E-R Model is typically represented graphicallygraphicallyusing anusing an E-R diagram E-R diagram

E-R modelE-R model

E-R models cannot describe everything in the E-R models cannot describe everything in the real-world applicationreal-world application

Not all information about the attributes appears Not all information about the attributes appears in the E-R diagram. Most of the information is in the E-R diagram. Most of the information is maintained in the data dictionary maintained in the data dictionary

The process of designing the E-R diagram is The process of designing the E-R diagram is iterativeiterative

E-R Diagrams: Entity ClassesE-R Diagrams: Entity Classes

Entity classes are represented by rectanglesEntity classes are represented by rectangleswith the name insidewith the name inside

Attributes are represented by ovals. Attributes are represented by ovals.

– key attributes are underlinedkey attributes are underlined

– Multi-valued attributes are double-linedMulti-valued attributes are double-lined

– Derived attributes are dashedDerived attributes are dashed

Example of an entity class Example of an entity class

lastName accountIdfirstName

numberRentals

balance

otherUsers

AttributeKey

Attribute

DerivedAttribute

Multi-valued

Attribute

Customer

address

zipcode

statecity

street

CompositeAttribute

ComponentAttribute

EntityClass

ExampleExample

EntityClass

Attribute

KeyAttribute

Video

videotapeId title genre

length

dateAcquired

rating

E-R diagrams: RelationshipsE-R diagrams: Relationships

A relationship is represented by a A relationship is represented by a rhombus (diamond) with the name insiderhombus (diamond) with the name insideThe name of a relationship is a verb The name of a relationship is a verb describing itdescribing itAdditional symbols of a relationship:Additional symbols of a relationship:– CardinalityCardinality– Optional/mandatory participationOptional/mandatory participation– Attributes of a relationshipAttributes of a relationship

Example of a relationshipExample of a relationship

RelationshipType

EntityClass

RelationshipAttribute

Store VideoOwns

costpurchase

Date

EntityClass

IsOwnedBy

AlternateRelationship

Name

ExampleExample

to-manyrelationship

role

Store VideoOwns

costpurchase

DateTo-one

relationshiprole

OptionalparticipationConstraint

MandatoryparticipationConstraint

1 M

IsOwnedBy

Modeling relations as entity classesModeling relations as entity classes

1Customer

MVideoRents

dateRented

costdateDue

MCustomer

MVideoPreviously

Rented

dateRented

costdate

Returned

Modeling relations as entity classesModeling relations as entity classes

A relationship can be A relationship can be modeled as an entity modeled as an entity classclass

Video1

Customer1

Has Rental1

MHas

costdateDue dateRented

Modeling relations as entity classesModeling relations as entity classes

Note cardinalities and participation Note cardinalities and participation constraintsconstraints– A Rental entity cannot exist without being A Rental entity cannot exist without being

related to both a customer and a videorelated to both a customer and a video

Problem occurs because Rental has no Problem occurs because Rental has no key attributekey attribute

Weak and Strong entitiesWeak and Strong entities

A A weak entity classweak entity class is is – An entity class with no key of its ownAn entity class with no key of its own– An entity class whose entities cannot exist An entity class whose entities cannot exist

without being related to other entitieswithout being related to other entities

An An identifying relationshipidentifying relationship type is type is– A relationship type that determines the keys A relationship type that determines the keys

of the weak entitiesof the weak entities

Weak and Strong entitiesWeak and Strong entities

Video1

Customer1

Has Rental1

MHas

IdentifyingRelationship

Type

Weak EntityClass

costdateDue dateRented

Owner EntityClass

More on Weak Entities and More on Weak Entities and RelationsRelations

An entity that is An entity that is identified by its identified by its relationship to other relationship to other entities is called a entities is called a weakweak entity and its entity and its class a class a weak entity weak entity classclass

DEPENDENT

EMPLOYEE

Ssn Name

Name BdateRelation

DEPENDENTS_OF

111111

1

N

More on Weak Entities and More on Weak Entities and RelationsRelations

The stronger entity class is called the The stronger entity class is called the identifyingidentifying or or ownerowner entity class entity class

The relationship that relates the weak entity The relationship that relates the weak entity class to its owner is called: class to its owner is called: identifyingidentifying relationshiprelationship

AA partial key partial key of a weak entity is a set of of a weak entity is a set of attributes that uniquely identifies weak entities attributes that uniquely identifies weak entities related to the same owner entityrelated to the same owner entity

ExampleExample

Entities:Entities:Customer (key: account , last name, first Customer (key: account , last name, first name, address, email, credit card, name, address, email, credit card, password)password)

Movie (key: id, title, genre, length)Movie (key: id, title, genre, length)

Sale (key: id, cost, date, credit card)Sale (key: id, cost, date, credit card)Shopping Cart (key: id, date)Shopping Cart (key: id, date)

ExampleExample

Relationship Relationship TypeType

Entity ClassEntity Class Entity ClassEntity Class Cardinality Cardinality RatioRatio

AttibutesAttibutes

PurchasesPurchases CustomerCustomer SaleSale one-to-manyone-to-many

IncludesIncludes SaleSale MovieMovie many-to-many-to-manymany

quantityquantity

SelectsSelects CustomerCustomer ShoppingCartShoppingCart one-to-manyone-to-many

IncludesIncludes ShoppingCarShoppingCartt

MovieMovie many-to-many-to-manymany

quantityquantity