Database

17 Mar 2017

Data is a raw facts before processed as an information. Database is a collection of data and Database Management System is a software package which stores and manages the system.

The use of DBMS is for the independences and efficient access, Data integrity and security, concurrency control, recovery and etc. It is better than stucking tons of data into file system.

Levels of Abstraction (Schema)

1. Physical schema : the files and indexed used(actual stored and form)
2. Conceptual schema : entire logical structure of the data
3. View : schema of what users need

Data independence

Applications insulated from how data is structured and stored.

• Logical data independence : Preocetion from changes from logicla structure of data
• Physical data independence : Protection from changes in physical structure of data

Transaction

Transaction is an operational unit of DBMS. There are 4 characteristic of transaction.

1. Atomic
2. Consistency
3. Isolated
4. Durability

Models

• E-R Model : Entity-Relationship Model
• R Model : Relational Model