Data Modeling and the Entity-Relationship Model

database
공개

2024년 10월 14일

Data and information

  • Data: raw facts. recorded facts
  • Information: meaningful context
  • Knowledge: information + 가치

What is information system?

  • System: a set of components that interact to achieve some purpose or goal
  • Information System: composed of hardware, software, data, procedures, people

System Analysis and Design

  • System analysis and design: process of creating and maintaining information systems
  • classic methodology: SDLC

SDLC (System Development Life Cycle)

SDLC
  1. System definitions: 예산 편상, 위험 분석, …
  2. Requirements analysis
  3. Component design
  4. Implementation
  5. System maintenance

database development process

  1. Requirements analysis
    input: the project plan
    output: a set of approved requirements -> data model (ER model로 conceptual design)
    source: Use cases, Business rules
  2. Component Design: Relational Database Design (상세 설계)
  3. Implementation

ER model

  • Entities
    • Entity class
    • Entity instance
  • Attributes: Data type, Properties(default, constraints)
  • Identifiers
    • unique
    • Nonunique: identifies a set of instances
  • Relationships
    • binary relationship
      • Maximum cardinality: 1:1(A has a B), 1:N(A has a set of B), M:N
      • Minimum cardinality: 0, 1
    • ternary relationship

Entit-Relationship Diagram

  • Entity classes: rectangle

  • Relationships: diamond

  • maximum cardinality: inside the diamond

  • minimum cardinality: oval or hash mark next to diamond

  • strong entity: 독자적으로 존재 가능. 강한개체 관계는 점선
    Non-ID-dependent: identifier에 다른 entity의 identifier가 포함되어 있지 않음. 점선으로 표기(non-identifying relationship)

  • weak entity: 약, 강 관계는 실선. IS: rounded square, traditional: 2 layer square
    ID-dependent: identifier에 다른 entity의 identifier가 포함되어 있음. 실선으로 표기(identifying relationship)

  • associative entity: relationship이 entity로 변환된 것.
    Many-to-many relationship을 2개의 1:N으로 변환

  • super type, sub type: 상속관계. sub type is a super type

    • exclusive: Discriminator attribute가 필요함
    • inclusive

  • recursive relationship

  • Business rule: build-in constraints, trigger, stored procedure, application code로 구현 가능

  • data model validation: form, report를 이용한 prototyping

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