What is Database?

Database

• Organized collection of inter-related data that models some aspect of the real-world.
• Databases are the core component of most computer applications.

---

Flat File Strawman

(strawman은 잘 동작하지 않을 것을 의미함.)

• Store our database as comma-separated value(CSV) files that we manage ourselves in our application code.
  • Use a separate file per entity.
  • The application must parse the files each time they want to read/update records.

---

Flat Files: Data Integrity

• 각 앨범마다 정확한 아티스트가 기재되었는지 어떻게 보장?
• 앨범의 연도를 잘못 기재했다면?
• 아티스트가 여러 명이라면?
• 아티스트가 삭제되었다면?

---

Flat Files: Implementation

• 특정한 앨범을 어떻게 찾는가?
• 동일한 데이터베이스를 사용하여 새로운 앱을 만들고 싶다면?
• 두 스레드가 동일한 시간에 동일한 파일에 접근한다면?

---

Flat Files: Durability

• 기계가 망가졌다면?
• 데이터베이스를 동일한 기계에 복제하고 싶다면?

---

Database Management System

• A database management system (DBMS) is software that allows applications to store and analyze information in a database. + (위의 문제들을 해결해줌.)
• A general-purpose DBMS supports the definition, creation, querying, update, and administration of databases in accordance with some data model.

---

Data Models

• A data model is a collection of concepts for describing the data in a database.
• A schema is a description of a particular collection of data, using a given data model.

---

Relational Model

• The relational model defines a database abstraction based on relations to avoid maintenance overhead. (그냥 표)
• Key tenets:
  • Store database in simple data structures(relations).
  • Physical storage left up to the DBMS implementation.
  • Access data through high-level language, DBMS figures out best execution strategy.

---

• Structure: The definition of the database’s relations and their contents.(타입도 정의해줘야 함.)
• Integrity: Ensure the database’s contents satisfy constraints.(제약조건도 걸 수 있음.)
• Manipulation: Programming interface for accessing and modifying a database’s contents.(데이터베이스를 고치거나 받아오는 인터페이스 제공)

---

• Relation model은 unordered set(순서 상관x)
• Tuple (순서쌍 → 순서 중요)

---

Relation Model: Primary Keys

• Primary Keys(기본키): 튜플을 구분할 수 있는 키(like 학번)
• _ 줄이 그어져 있음.
• 기본키 두개 가능

---

Relation Model: Foreign Keys

• Foreign Keys(외래키): 다른 테이블의 값을 참조하도록 되어 있다.

---

Databases are ubiquitous.

Relational algebra defines the primitives for processing queries on a relational database.