Database Systems

DBMS: database management system

Topics on database systems:

• DB systems concepts
• realtional  model
• SQL
• E-R model
• DB design(RDB design)
• storage and file structure
• indexing
• Query Processing & Optimization
• Transaction
• Concurrency Control
• Recovery

Database Systems & DB design

Drawbacks of using file systems to store data:

• Data redundancy and inconsistency
• Difficulty in accessing data
• Data isolation
• Integrity problems
• Atomicity of updates 
• Concurrent access by multiple users
• Security problems
• Data Dependence Problem

View of Data

• View level: describes only part of the entire database. Views can also hide information for security purpose
• Logical leve: describe what data stored in database, and what relationship among the data
• Physical level: describe how data are actually stored

DB language

• DDL(Data definition language)

Data dictionary contains metadata: database schema、Integrity constrains、Authorization

• DML(Data manipulation language) 操控

DML also konown as query language

Two classes of languages: Procedural、Declarative 

SQL is the most widely used query language

• DCL

Query Processing: Parsing and translation、Optimization、Evalation

Query Processing Procedure: