Ch.5 Entity-Relationship Model (1)

Peter P. Chen 1976

Ch5 E-R Model Database System 2

What to Learn Database System Overview Entity-Relationship diagram Relational Data Model

Structure & Constraints SQL language

How to use Commercial DBMS’s MS Access MS SQL Server

Normalization ( 정규화 ) Transaction & Concurrency ( 동시성 )

Ch5 E-R Model Database System 3

What to learn Database design Entity-Relationship Diagrm

Entity Attribute Relationship Diagram 그리기

Logical database design 7 steps

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Database Design (1)

logical schema

datamodeling

Real World

system boundary

E-R diagram

conceptualmodeling

physical schema

datastructuring

conceptual world

computer world

stored database

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Database Design (2) p.258

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Database Design (3) Conceptual design

ERD (entity-relationship dia-gram)

Logical design ERD->Relations mapping Normalization

logical schema Physical design

physical schema Transaction design etc.

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E-R model, Chen, 1976 (En-tity) Entity

any distinguishable object to be represented in the databasevisible vs. invisible entities

(student, book, department, course)regular vs. weak entities

(employee, building, dependent, apart-ment)

p. 271

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E-R model (Attribute) Attribute

a characteristic of an object with which we describe the ob-ject

Attributes are characteristics common to all the entities or relationships of a given type

simple vs. composite attributes key attribute single-valued vs. multi-valued attributes stored (base) vs. derived attributes

판매액 = 판매량 * 가격

p. 269

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E-R model (Relationship) Relationship

an association among entities degree

number of entity types involved in the relation-ship

p. 274

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E-R Model (Relationship) example of ternary relationship

a) supplier S1 supplies part P1b) supplier S1 supplies to project J1c) project J1 uses part P1

Above three statements do not say thatd) supplier S1 supplies P1 to project J1.

If S1-P2-J1, S1-P1-J2, S2-P1-J1 (S1-P1), (S1-J1), (P1-J1)

statements a), b), c) are still correct but we cannot validly infer statement d).

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E-R Model (Relationship) cardinality

maximum number of elements on each side of a relationship

p. 276

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E-R Model (Relationship) examples of cardinality

one-to-one학과 ←학과장→교수

남편←→아내 , 교수←→연구실 one-to-many

학과←소속→교수 , 학생←지도→교수 ,판매원←담당→거래처

many-to-many 학생←수강→과목 , 부품 ←구성→부품 ,

학생←구독→신문

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E-R Model (Relationship) total vs. partial participation

학생←지도→교수 , 교수←사용→연구실 Notes

entity vs. attributepublisher (pub_id, pub_name, location, phone)book (book_id, title, author, pub_date, pub-lisher)

entity vs. relationship물품←주문→고객 : 주문 as a relationship

주문← ( 구매 또는 결재 )→ 고객 : 주문 as an entity

주문 ← 구성 → 물품 : 주문 구성

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E-R Model (Notation) p. 285 Notation

p. 285

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E-R Model (Other Notation) Crow’s feet Notation (p .287)

Ch5 E-R Model Database System 16

E-R Model (Other Notation) Crow’s feet Notation (p .287)

Ch5 E-R Model Database System 17

E-R Model (Other Notation) Crow’s feet Notation (p .289)