DBMS 2021
===

- `Database`:collection of related data
- `Data`
- `meta-data`: 描述有哪些data的Data
- `Mini-World`: Under real world
- `Entity`(Entities)
- Must be ALL CAPITAL NAME
- `DBMS`:Database Management System
- `Self-contained`:
- `Insulation between programs and data`
- `Data Abstraction`
- Support multiple views of the dat`
- `Database System`: `DBMS` + `Data`
- `DDL`:
- `DML`:
- Left outer join
- work of a tool developer
- referential integrity constrain