1 R. Ching, Ph.D. MIS California State University, Sacramento Week 9 October 24 Modeling with ERDModeling…

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R. Ching, Ph.D. • MIS • California State University, Sacramento

Week 9Week 9October 24October 24

• Modeling with ERDModeling with ERD

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Entity Relationship (ER) ModelEntity Relationship (ER) Model(applies to relational data model)(applies to relational data model)

• High-level conceptual model High-level conceptual model – Describes the structure of the database, and the Describes the structure of the database, and the

associated retrieval and update transactions on the associated retrieval and update transactions on the databasedatabase

– Composed of Composed of • Entity types Entity types • Relationship typesRelationship types• AttributesAttributes

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ERD NotationERD Notation

Music_categoriesMusic_categoriesmusic_category_code {PK}music_category_code {PK}music_category_titlemusic_category_title

CDsCDs

stock_number {PK}stock_number {PK}CD_titleCD_titleartistartistmusic_category_code music_category_code record_label_coderecord_label_code

Entity typeEntity typePrimary keyPrimary key

AttributesAttributes

Relationship nameRelationship name

ClassifyClassify

1..11..1 0..*0..*

Relationship typeRelationship type

Degree of the Relationship: BinaryDegree of the Relationship: Binary

Multiplicity (constraint)Multiplicity (constraint)

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ERD NotationERD NotationAlternativelyAlternatively

Music_categoriesMusic_categoriesMusic_category_codeMusic_category_codeMusic_category_titleMusic_category_title

CDsCDs

Stock_numberStock_numberCD_titleCD_titleArtistArtistMusic_category_code Music_category_code Record_label_codeRecord_label_code

ClassifyClassify

Entity typeEntity typePrimary key (underscored)Primary key (underscored)


Relationship typeRelationship typeRelationship nameRelationship name

ManyMany(crows feet)(crows feet)

CardinalityCardinality

ZeroZero(circle)(circle)

MinimumMinimum(inside)(inside)MaximumMaximum

(outside)(outside)

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ERDERD

• Entity type – A group of objects with the same properties, Entity type – A group of objects with the same properties, which are identified by the enterprise as having an which are identified by the enterprise as having an independent existenceindependent existence

• Relationship type – A set of meaningful associations Relationship type – A set of meaningful associations among entity typesamong entity types

• Attributes – A property of an entity or a relationship typeAttributes – A property of an entity or a relationship type

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Degree of Relationship TypeDegree of Relationship Type

• The number of participating entity types in a relationshipThe number of participating entity types in a relationship• Binary (two entity types)Binary (two entity types)

• Ternary (three entity types)Ternary (three entity types)

EmployeeEmployee Employee AwardsEmployee AwardsReceivesReceives

1..11..1 0..10..1

EmployeeEmployee Emp_BenefitsEmp_Benefits

Emp_TaxEmp_Tax

Net payNet pay

ReceivesReceives

Attribute of a relationship typeAttribute of a relationship type

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Recursive RelationshipRecursive Relationship

• A relationship type where the same entity participates A relationship type where the same entity participates more tan once in different rolesmore tan once in different roles

EmployeeEmployee

ManagesManages

ManagerManager

StaffStaff

A manager is an employeeA manager is an employee

Managers and staff are employees.Managers and staff are employees.

Staff are managed Staff are managed by managersby managers

1..*1..*

0..*0..*

Role name indicates the purpose an Role name indicates the purpose an entity type plays in a relationship typeentity type plays in a relationship type

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Property of an entity or relationship typeProperty of an entity or relationship type

• Attribute domainAttribute domain– Set of values that may be assigned to a single-valued Set of values that may be assigned to a single-valued

attributeattribute

Cust_account Cust_name Cust_address Cust_phone Soc_Sec_NumCust_account Cust_name Cust_address Cust_phone Soc_Sec_NumCustomersCustomers

Cust_account Current_balance Credit_limit Active_date Expire_dateCust_account Current_balance Credit_limit Active_date Expire_dateCustomer_AccountsCustomer_Accounts

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Attributes of AttributesAttributes of Attributes

• Simple (atomic attributes) - composed of a single Simple (atomic attributes) - composed of a single componentcomponent

• Composite - composed of multiple componentsComposite - composed of multiple components• Single valued - one value for an entitySingle valued - one value for an entity• Multi-valued - one or more values for an entityMulti-valued - one or more values for an entity• Derived - value derived from a related attribute or set of Derived - value derived from a related attribute or set of

attributesattributes

Student_ID Semester Course_IDStudent_ID Semester Course_ID

Student_ID FName MName LNameStudent_ID FName MName LName

Multi-valuedMulti-valued

Single-valuedSingle-valued

More than one More than one semestersemester, more than one , more than one course_idcourse_id

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Attribute DomainAttribute Domain

Cust_account Cust_name Cust_address Cust_phone Soc_Sec_NumCust_account Cust_name Cust_address Cust_phone Soc_Sec_Num

CustomersCustomers

JohnJohnWilliamWilliamAnitaAnitaHomerHomer

BrownBrownTellTellBreakeBreakeSimpsonSimpson

• On an ER model, On an ER model, should customer should customer name be shown as a name be shown as a composite or simple composite or simple attribute? attribute?

• What is the attribute What is the attribute domain of domain of Cus_name?Cus_name?

Cust_first_nameCust_first_name Cust_last_nameCust_last_name

CompositeComposite

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Derived AttributesDerived Attributes

• Derived - value derived from a related attribute or set of Derived - value derived from a related attribute or set of attributesattributes

Units Units xx Grade = Grade point Grade = Grade point

Student_ID Semester Course_ID Units Grade Grade_pointStudent_ID Semester Course_ID Units Grade Grade_pointStudent_ID Semester Course_ID Units Grade Grade_pointStudent_ID Semester Course_ID Units Grade Grade_point

Student_ID Semester Course_ID Units Grade Grade_pointStudent_ID Semester Course_ID Units Grade Grade_point

Derived attributeDerived attribute

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Attributes as KeysAttributes as Keys

Primary keyPrimary key

Candidate keyCandidate key

• Alternate key - candidate that can also be used to access Alternate key - candidate that can also be used to access an entityan entity

• Composite key - composed of multiple attributes Composite key - composed of multiple attributes (components)(components)

Uniquely identifies an entityUniquely identifies an entity

• Keys cannot change their values Keys cannot change their values (good for the life of the entity)(good for the life of the entity)

• An An efficientefficient means for identifying means for identifying an entityan entity

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Attribute Diagrammatic RepresentationAttribute Diagrammatic Representation

Composite attributeComposite attribute

CustomersCustomers

Cust_account {PK}Cust_account {PK}Cust_nameCust_name First_nameFirst_name Middle_nameMiddle_name Last_nameLast_nameCust_addressCust_address Street_numberStreet_number Zip_code (fk)Zip_code (fk)Cust_phoneCust_phoneSoc_sec_numSoc_sec_num

Composite attributeComposite attribute

KeyKey

Foreign keyForeign key

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Attribute Diagrammatic RepresentationAttribute Diagrammatic Representation

Composite keyComposite key

Customer_PurchasesCustomer_Purchases

Cust_account {PK}Cust_account {PK}Transaction_number {PK}Transaction_number {PK}DateDateStore_numberStore_numberPayment_typePayment_type


A customer may have more than one purchaseA customer may have more than one purchase


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Strong vs. Weak Entity TypesStrong vs. Weak Entity Types

• Strong Entity Type – An entity type that is not existence-Strong Entity Type – An entity type that is not existence-dependent on some other entity typedependent on some other entity type– Often referred to as Often referred to as parentparent, , ownerowner or or dominantdominant entities entities

• Weak Entity Type – An entity type that is existence-Weak Entity Type – An entity type that is existence-dependent on some other entity type.dependent on some other entity type.– Often referred to as Often referred to as childchild, , dependentdependent or or subordinate subordinate

entities entities

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Definition of a Weak Entity TypeDefinition of a Weak Entity Type

“ “An entity type that borrows all or part of its primary key. An entity type that borrows all or part of its primary key. Identifying relationships indicate the entity types that Identifying relationships indicate the entity types that supply components of the borrowed primary key.”supply components of the borrowed primary key.”

Mannino, 1999Mannino, 1999

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Customer_accountsCustomer_accounts

AccountNumber {PK}AccountNumber {PK}FirstNameFirstNameMiddleNameMiddleNameLastNameLastNameAddressAddressZipCodeZipCodeMembershipDateMembershipDate


AccountNumber {PK}AccountNumber {PK}StoreNumber {PK}StoreNumber {PK}TransactionDate {PK}TransactionDate {PK}TransactionNumber {PK}TransactionNumber {PK}PaymentTypePaymentType

PurchasePurchase

1..11..1 0..*0..*

Which is the strong and weak entity type?Which is the strong and weak entity type?How can you tell?How can you tell?

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Customer_accountsCustomer_accounts

AccountNumber {PK}AccountNumber {PK}FirstNameFirstNameMiddleNameMiddleNameLastNameLastNameAddressAddressZipCodeZipCodeMembershipDateMembershipDate


AccountNumber {PK}AccountNumber {PK}StoreNumber {PK}StoreNumber {PK}TransactionDate {PK}TransactionDate {PK}TransactionNumber {PK}TransactionNumber {PK}PaymentTypePaymentType

PurchasePurchase

1..11..1 0..*0..*

Which is the strong and weak entity type?Which is the strong and weak entity type?How can you tell?How can you tell?

Existent-dependenceExistent-dependence Also a FKAlso a FK

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Attributes of Relationship TypesAttributes of Relationship Types

• Attributes produced through relationship types (i.e., not Attributes produced through relationship types (i.e., not retained in the entity types)retained in the entity types)

CustomerAccountsCustomerAccounts

AccountNumberAccountNumber……

CustomerFlightsCustomerFlights

AccountNumber {PK}AccountNumber {PK}TransactionDate {PK}TransactionDate {PK}IntineraryNumber {PK}IntineraryNumber {PK}……

ReserveReserve1..11..1 0..*0..*

NumberOfItinerariesNumberOfItineraries Derived attributeDerived attribute

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Structural ConstraintsStructural Constraints

• Multiplicity – Number of possible occurences of an entity Multiplicity – Number of possible occurences of an entity type that may relate to a single occurrence of an associated type that may relate to a single occurrence of an associated entity type through a particular relationship typeentity type through a particular relationship type– One to one (1:1)One to one (1:1)– One to many (1:*)One to many (1:*)– Many to many (*:*)Many to many (*:*)

• Cardinality and participation constraintsCardinality and participation constraints– Cardinality – Describes the maximum number of Cardinality – Describes the maximum number of

possible relationship occurrences for an entity possible relationship occurrences for an entity participating in a given relationship typeparticipating in a given relationship type

Defined by business rulesDefined by business rules

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Cardinality and Participation ConstraintsCardinality and Participation Constraints

• Cardinality – Describes the maximum number of Cardinality – Describes the maximum number of possiblepossible relationship occurrences for relationship occurrences for anan entity participating in a entity participating in a given relationship typegiven relationship type

• Participation – Determines whether all or only some entity Participation – Determines whether all or only some entity occurrences participate in a relationshipoccurrences participate in a relationship– 1:1 (1..1) minimum is one – mandatory participation1:1 (1..1) minimum is one – mandatory participation– 0:1 (0..1) minimum is zero – optional participation0:1 (0..1) minimum is zero – optional participation

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• 1:1 (1:1 (one to oneone to one))– Each entity in Each entity in XX is associated with at most one entity in is associated with at most one entity in YY

and conversely each entity in and conversely each entity in YY is associated with at most is associated with at most one entity in one entity in XX

• 1:* (1:* (one to manyone to many))– Each entity in Each entity in XX can be associated with many entities in Y can be associated with many entities in Y

but each entity in but each entity in YY is associated with is associated with at mostat most one entity in one entity in XX..

• *:* (many to many)*:* (many to many)– Each entity in Each entity in XX can be associated with many entities in can be associated with many entities in YY

and each entity in and each entity in YY can be associated with many entities in can be associated with many entities in XX..

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CustomersCustomersCustomer_ID {PK}Customer_ID {PK}Customer_nameCustomer_nameCustomer_addressCustomer_addressZip_codeZip_code

OwnOwn

A customer owns a A customer owns a minimum and maximum minimum and maximum of of oneone account account

AccountsAccountsAccount_number {PK}Account_number {PK}Customer_ID {FK}Customer_ID {FK}Account_typeAccount_typeCurrent_balanceCurrent_balance

An account is owned An account is owned by a minimum and by a minimum and maximum of maximum of oneone customercustomer

1:1 Relationships1:1 RelationshipsStrong entity typeStrong entity type Weak entity typeWeak entity type

Mandatory Mandatory participationparticipation

NoteNote. This would be avoided in the logical design, but could be implemented in . This would be avoided in the logical design, but could be implemented in the physical.the physical.

1..11..1 1..11..1

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OwnOwn

A customer owns a A customer owns a minimum one and minimum one and maximum of many maximum of many accountsaccounts


1:M Relationships1:M RelationshipsStrong entity typeStrong entity type Weak entity typeWeak entity type

Mandatory Mandatory participationparticipation

An account is own by a An account is own by a minimum and maximum minimum and maximum of one customerof one customer

1..11..1 1..*1..*

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• *:* (many-to-many) relationship if a customer can own *:* (many-to-many) relationship if a customer can own more than one account (e.g., revolving, long-term), and more than one account (e.g., revolving, long-term), and one account can have more than one owner (e.g., joint one account can have more than one owner (e.g., joint account).account).


OwnOwn

A customer owns a A customer owns a minimum one and minimum one and maximum of many maximum of many accountsaccounts


An account is own by a An account is own by a minimum of one minimum of one customer and maximum customer and maximum of many customersof many customers

1..*1..* 1..*1..*

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Video_categoriesVideo_categoriesCategory_code {PK}Category_code {PK}Category_titleCategory_title

VideosVideos

Stock_number {PK}Stock_number {PK}Video_titleVideo_title……Category_code {FK}Category_code {FK}Distributor_code {FK}Distributor_code {FK}

ClassifyClassify

Entity typeEntity typePrimary keyPrimary key



ManyManyCardinalityCardinality ZeroZeroMinimumMinimum

MaximumMaximum

1..11..1 0..*0..*

For an occurrence of videos, For an occurrence of videos, there may exist one and only there may exist one and only one video category.one video category.

For an occurrence of video For an occurrence of video categories, there may exist categories, there may exist zero to many videos.zero to many videos.

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VideosVideos


ClassifyClassify

1..11..1 0..*0..*

DistributorsDistributorsDistributor_code {PK}Distributor_code {PK}Distributor_nameDistributor_name

0..*0..*

1..11..1

ReleaseRelease

Video categories classify videosVideo categories classify videos

Distributors release videosDistributors release videos

For an occurrence of distributors, For an occurrence of distributors, there are zero to many videosthere are zero to many videos

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VideosVideos


ClassifyClassify

1..11..1 0..*0..*


0..*0..*

1..11..1

ReleaseRelease

Video categories classify videosVideo categories classify videos

Distributors release videosDistributors release videos

For an occurrence of videos, there is For an occurrence of videos, there is one and only one video categoryone and only one video category

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VideosVideos


ClassifyClassify

1..11..1 0..*0..*


0..*0..*

1..11..1

ReleaseReleaseAttribute of the Attribute of the relationship typerelationship type

Number_of_videos_Number_of_videos_releasedreleased

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ERD NotationERD NotationAlternate NotationAlternate Notation


CDsCDs


ClassifyClassify

Entity typeEntity typePrimary key (underscored)Primary key (underscored)



ManyMany(crows feet)(crows feet)


ZeroZero(circle)(circle)

MinimumMinimum(inside)(inside)MaximumMaximum

(outside)(outside)

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ERD NotationERD NotationAlternate NotationAlternate Notation


CDsCDs


ClassifyClassify

Entity typeEntity type

Weak entity typeWeak entity type(all four corners)(all four corners)

Minimum cardinality of oneMinimum cardinality of one((a music category has to have at least one CDa music category has to have at least one CD))

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ERD NotationERD Notation Alternative NotationAlternative Notation


CDsCDs


ClassifyClassify

Record_label_codeRecord_label_codeRecord_labelRecord_label

Record_labelsRecord_labels

ProduceProduce

A record label is related to A record label is related to a minimum of zero and a minimum of zero and maximum of many CDsmaximum of many CDs

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ERD NotationERD Notation Alternative NotationAlternative Notation


CDsCDs


ClassifyClassify



ProduceProduceA CD is related to a A CD is related to a minimum and maximum of minimum and maximum of one record labelone record label

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ERD NotationERD NotationAlternative NotationAlternative Notation


CDsCDs


ClassifyClassify



ProduceProduceQuantity_producedQuantity_produced

Attribute of a relationshipAttribute of a relationship

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Documents

1 R. Ching, Ph.D. MIS California State University, Sacramento Week 9 October 24 Modeling with ERDModeling…