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

Ch5 E-R Model Database System 4 Database Design (1) logical schema data modeling Real World system boundary E-R diagram conceptual modeling physical schema data structuring conceptual world computer world stored database

Ch5 E-R Model Database System 5 Database Design (2) p.258

Ch5 E-R Model Database System 6 Database Design (3) Conceptual design ERD (entity-relationship diagram) Logical design  ERD->Relations mapping  Normalization logical schema Physical design physical schema Transaction design etc.

Ch5 E-R Model Database System 7 E-R model, Chen, 1976 (Entity) Entity any distinguishable object to be represented in the database visible vs. invisible entities (student, book, department, course) regular vs. weak entities (employee, building, dependent, apartment) p. 271

Ch5 E-R Model Database System 8 E-R model (Attribute) Attribute a characteristic of an object with which we describe the object 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

Ch5 E-R Model Database System 9 E-R model (Relationship) Relationship an association among entities  degree number of entity types involved in the relationship p. 274

Ch5 E-R Model Database System 10 E-R Model (Relationship) example of ternary relationship a) supplier S1 supplies part P1 b) supplier S1 supplies to project J1 c) project J1 uses part P1 Above three statements do not say that d) 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).

Ch5 E-R Model Database System 11 E-R Model (Relationship) cardinality maximum number of elements on each side of a relationship p. 276

Ch5 E-R Model Database System 12 E-R Model (Relationship) examples of cardinality  one-to-one 학과 ← 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

Ch5 E-R Model Database System 13 E-R Model (Relationship) total vs. partial participation 학생 ← 지도 → 교수, 교수 ← 사용 → 연구실 Notes  entity vs. attribute publisher (pub_id, pub_name, location, phone) book (book_id, title, author, pub_date, publisher)  entity vs. relationship 물품 ← 주문 → 고객 : 주문 as a relationship 주문 ←( 구매 또는 결재 )→ 고객 : 주문 as an entity 주문 ← 구성 → 물품 : 주문 구성

Ch5 E-R Model Database System 14 E-R Model (Notation) p. 285 Notation p. 285

Ch5 E-R Model Database System 15 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)