Chapter1 Introduction to Databases

Chapter 1 Introduction to Databases

1.1 Introduction

For the purpose of this discussion,we consider database to be a collection of relate data and a database base management system to be the software that manage and control access to the database.

1.2 Traditonal File-Based Systems
1.2.1 File-Based Approach

File-based System:A collection of application programs that perform  services for end-users  ,such as the production of reports.Each program defines

and manages its own data.

Consider the effort that would be required to answer the following

question:

what is the annual total for staff salaries?

What is the expected monthly net income for the next financial year?

The decentralized approach was taken.

1.2.2 Limitation of File-based Approach

separation and isolation of data

duplication of data

data dependence

incompatitile file formats

fixed queries of application programs

1.3 Database Approach

1.3.1 The Database

Database:

A shared collection of logically related data and its description,designed to meet the information needsof an organization.

1.the approach taken with database systems,...,is similar to the approach taken in modern software development

where an internal definition of an object and a separate external definition are provided.The users seeonly the external definition and are unaware of how the object is defined about how it functions.

One advantage of this approach known as data abstraction, is that we can change the internal defition of an object without affecting the users of the object.

Another expression in definition of a database that we should explain is “logical related”....

An entity is(=) a distinct object in the organization that is to be represented in the database.

An attribute is(=) a property that describe some aspect of the object that we wish to record, and a relationship is a association between entities.

1.3.2 The database Management System

DBMS: A software system that enables users to define,create,and control access to the database.

Provide the following facilities:

• it allow users to define the database , usually through a DataDefinition Language(DDL).The DDL allows users to specify the data type and structures and the constraints on the data to be stored in the database.

• It allow users to insert , update, delete,and retrieve data from the database,usually through the Data Manipulation Language(DML)。The most common query language is the Structure Query language.

• It provide the control access to the database,for example,include:

security system

integrity system

concurrency system

recovery system

1.3.3(Database) Application Programs

A computer program that interacts with the database by issuing an appropriate request to the DBMS.

Views: a DBMS provides another facility known as a view mechanism, which allow each users to have his or herown view of the database.

1.3.4 Components of the DBMS Environment

Hardware
Software

Data

Procedure:refer the instructions and rules that govern the design and the use of the database .

1.4 Roles in the Database Environment

• data and database administrator

• database designer

• application developer

• end-users

1.4.1 Data and Database Administrators

Data Administrator: responsible for management of the data source.

Database Administrator: responsible for the physical realization of the database.

1.4.2 Database designers
logical database designer is concerned with identify the data,the relationship between the data , and the constraints on the data that is to be

  stored in the database.

Physical database designer:decide how the logical database design to be physical realized.