[DB] Schema, DDL, DML 정리

The goal of Three-schema architecture is to separate the user applications and the physical DB.

→ 목표 = 사용자 애플리케이션과 물리적 DB를 분리하여 DB의 독립성 확보.

 

Internal schema describes the physical storage structure of the DB.

Conceptual schema describes the structure of the whole DB for a community of users.

External schema describes the part of the DB that a particular user group is interested in and hides the rest of the DB from that user group.

 

The processes of transforming requests and results between levels are called Mapping.

 

Logical data independence(LDI) is the capacity to change the Conceptual schema without having to change External or app.

Physical data independence is the capacity to change the Internal schema without having to change the Conceptual schema.

 

In DBMS, one language, called the DDL is used by the DBA and by DB designers to define schemas.

A high-level DML used in a stand-alone interactive manner is called a query language.

 

In general, both retrieval and update commands of a high-level DML may be used interactively and are hence considered part of the Query language.

→ 일반적으로 고급 DML의 검색 명령과 업데이트 명령은 모두 대화식으로 사용될 수 있으므로 쿼리 언어의 일부로 간주된다.