Introduction - Database system concepts

A database management system (DBMS) consists of a collection of interrelated data and a set of programs to access that data. The collection of data is usually referred to as the database. The database contains information about one particular enterprise. The primary goal of a DBMS is to provide an environment that is both convenient and efficient to use in retrieving information from and storing information into the database.

Database systems are designed to manage large bodies of information. The management of data involves both the definition of structures for the storage of information and the provision of mechanisms for the manipulation of information. In addition, the database system must provide for the safety of information stored in the database, despite system crashes or attempts at unauthorized access. If data is to be shared among several users, the system must avoid possible anomalous results.

Because of the importance of information in most organizations, the database is a valueable resource. This has led to the development of a large body of concepts and techniques for the efficient management of data. In this champter, we present a brief introduction to the principles of database systems.

Purpose of Database Systems
· Data redundancy and inconsistency
· Difficulty in accessing data
· Data isolation
· Multiple users
· Security problems
· Integrity problems

Data Abstraction
· Physical level
· Conceptual level
· View level

Data Models
· Object-Based Logical Models
· Record-Based Logical Models
· Physical Data Models

Instances and Schemes

Data Independence

Data Definition Language

Data Manipulation Language

Database Manager
· Interaction with the file manager
· Integrity enforcement
· Security enforcement
· Backup and recovery
· Concurrency control

Database Administrator
· Scheme definition
· Storage structure and access method definition
· Scheme and physical organization modification
· Granting of authorization for data access
· Integrity constraint specification

Database Users
· Application programmers
· Casual users
· Naïve users
· Specialized users

Overall System Structure
· File manager
· Database manager
· Query processor
· DML precompiler
· DDL complier