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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.
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