Client/Server Computing

Client/Server Computing Information processing is distributed

among several workstations and servers on a network, with each function being assigned to the environment that is best suited to perform it. The client initiates the requests and the server responds.

Consolidate the virtues of traditional time-shared mainframe and mini-computer paradigms with the advantages of personal computers, workstations, and local area networks

Components of Client/Server Computing Three interrelated components

Client - the front-endServer - the back-endNetwork - the middle ware

M:N relation between clients and servers.

A Basic Client/Server Computing Model

Client/Server Architecture The client is any computer process that

requests services from the server. It is also known as the front-end application.

The server is any computer process providing services to the clients. The server is also known as the back-end application.

The communication middleware is any computer process(es) through which clients and servers communicate. It is also known as middleware or communications layer.

How Client And Server Components Interact

Two levels of communications middleware The physical level deals with the

communications between client and server computers (computer to computer).

The logical level deals with the communications between client and server processes (process to process).

Interaction Between Client/Server Middleware Components

Database Middleware Components Application programming interface

(API) interfaces with the client application.

The database translator translates the SQL requests into the specific database server syntax.

The network translator manages the network communications protocols.

Database Middleware Components

Three Main Benefits of Using Middleware Access multiple databases Database server-independent Network protocol-independent

Middleware Accessing Multiple Database Servers

Application Functional Logic Components

Typical Logic Component Placement

The presentation logic is always placed on the client side.

The I/O processing logic may be placed on the client side or on the server side, but more commonly on the client side.

The business logic can also go either to the client or the server, but usually on the client side.

The data management logic can also be placed on either the client or the server side, but normally on the server side as part of the application code.

The data manipulation logic is most commonly located on the server side.

Functional Logic Splitting In Four Client/Server Architectural Styles

Microsoft SQL Client/Server Connection

MicrosoftSQL(server version)

MicrosoftSQL(workstation version)

LAN

Client PC ServerComputer

Microsoft SQL Client/Server Connection

At the server site, DBA creates a SQL database for the user

At the client site, the user can make remote registration and logon to access SQL database stored on the server

MicroSoft SQL Server SQL Server registration

local and remote servers SQL Server security control

Windows NT authenticationSQL user authentication

User access privilege specification

SQL Client/Server Connection

Buscom SQLserver

Local SQL server

MGD B106 Computer or your own PC

Remote SQL server registration

User authentication using

your user name and password

Local SQL server registration

Import/export

Backup disk

Backup/restore

Yourdatabase created by DBA

You create your own

database

Linking to SQL Server from Access

MicrosoftSQL

MicrosoftAccess

Internet

ODBC

Client 1 DB Server

MicrosoftAccess

ODBC

Client 2

LAN

ODBC

Web Server

ASP

ODBC Open Database Connectivity DBMS-independent means for

processing relational database data ORACLE SYBASE INFORMIX

Page 342

ODBC Terminology Data source: the database, its

associated DBMS, operating system, and network platform

Driver manager: intermediary between the application and DBMS drivers

Driver: processes ODBC requests and submits SQL statements to a data sourcePage 343

ODBC Architecture

Page 343Figure 13-5 © 2000 Prentice Hall