The Entity-Relationship Model

Semantic Model -

Semantic Model Entity Property EntityProperty Entity IdentityRelation Entity Type 2 Entity Type Subtype Entity Type Entity

- (Entity-Relationship Model)- -Entity Property Relation Entity SubType SuperType

Entity Relationship Diagram ER

ER ModelER-Model Peter Pin Shan Chen

(Weak Entity)

ER model()

(Weak Relationship) primary key

ER model()

()

ER model()E1E2R

(derived attribute)

E2 E1 E2 total participation E1

ER model()E1E2R

E1 E2 E2 partial participation E1

E-R diagramEntity Customer, department, division, employee building, room, branch, campus book, machine, product, raw material invoice, order, registration, reservation account, bond, course, stock

E-R diagramEntity 2 Strong Entity Weak Entity

E-R diagramAttributes Entity attribute entity -

E-R diagramAttribute 6 1. Simple Attribute: attribute sex salary atomic attribute2. Key Attribute : ID_people , ID_student

Attribute Domain : attribute

E-R diagramAttribute 6 3. Composite Attribute: attribute address street, area, city zipcode

E-R diagramAttribute 6 4. Single-Value Attribute: entity branch attribute Bno Single-Value Attribute B3 Bno (Branch_no)

E-R diagramAttribute 6 5. Multi-value Attribute: attribute

E-R diagramAttribute 6 6. Derived Attribute: entity attribute entity attribute attribute /// attribute

E-R diagramRelation () Entity 2 entity entity attribute entity entity

Cardinality Constraints (ratio) (one-to-one relationship) : entity entity

Cardinality Constraints (ratio) (one-to-many relationship): entity entity

Cardinality Constraints (ratio) (many- to- many relationship): entity

entity entity (Cardinality of Relationships)One to One relationship (1 : 1)One to Many relationship (1 : M)Many to Many relationship (M : M)

Mapping CardinalitiesOne to oneOne to many

Mapping Cardinalities Many to oneMany to many

One to One Relationship

11

One to Many

1M

Many to Many

1 1

Entity(Degree of Relationship)Unary (Recursive) Relationship Binary Relationship 2 Ternary Relationship 3

Entity(Degree of Relationship) 1mUnaryMMMTernaryBinaryMM

Fan Trap EntityChasm Trap -

-Fan Trap Entity one-to-many

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-Chasm Trap entity entity 2 entity

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-- Entity Entity Entity Entity-

-- 2

ER 1. CustomerCusIDCusNameCusSurNameCusAddCustomer (CusID, CusName, CusSurName, CusAdd)

ER ()2. 2.1 1 to 1 pk TeacherThIDThNameThSurNameTeacher (ThID, ThName, ThSurName)Faculty (FacID,FacName,ThID*)FacultyFacIDFacName11

ER ()2. 2.2 1 to M pk 1 M

CustomerCusIDCusNameCusSurNameCustomer (CusID, CusName, CusSurName)Orders (OID,OrderDate, ReqDate ,CusID*)OrdersOIDOrderDate1MReqDate

ER ()2. 2.3 NullCustomerCusIDCusNameCusSurNameCustomer (CusID, CusName, CusSurName)Orders (OID,OrderDate, ReqDate ,CusID*)OrdersOIDOrderDate1MReqDate

ER ()3. M to M PK PK Product (PID, PName, Price) Orders (OID,OrderDate, ReqDate ,CusID*)OrderDetail (OID*, PID*, Discount, Amount, UnitPrice) pk OrderDetail (id,OID*, PID*, Discount, Amount, UnitPrice)

ER ()4. PK PK Customer (CusID, CusName, CusSurName)CusCredit (CusID*, CreditNum)

ER ()5. PK PK PK Invoice (Inv no, Date)InvoiceDetail ( Inv no* ,Line)M