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Chapter 9

Client/ServerComputing

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Learning Objectives

After studying this chapter, you will be able to:

Describe client/server computing and the reasons for its growth

Compare and contrast client/server and LAN environments

Identify some popular client/server applications Summarize key advantages and disadvantages

of client/server systems

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What Is a Client/Server System?

A system that links a client and server through networks. The client requests the server for a given service and the server provides the service if a predetermined set of conditions is met.

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Client/Server System

The client computer sends a request for service to the server over a network.

If the client’s request is appropriate, the server provides the service.

Client Server

Networks

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Interactions between Client and Server

A number of rules guide the interactions between a client and a server When a server receives a request from a client, it

checks to see if the client is authorized A server can serve multiple clients at the same

time and, conversely, a client may request services from multiple servers

Client processes are independent of server processes

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Dumb Terminal/Host Processing

A client/server situation in which the server does all the processing work.

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Dumb Server

A client/server situation in which the server does not do any processing but delivers the data or files to the requesting client, which does all the processing.

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Front-end Software

Software that resides on the client and accesses data and programs from the server and then presents it in a user-friendly format for client users.

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Back-end Software

Software that resides on the server and helps to manage and protect the data and other files on the server.

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Middleware

Software that helps the client communicate with the server to ensure the smooth functioning of different components in a client/server system.

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Uses of Front-end, Back-end, and Middleware Software

Type of Software Who Uses Responsible for…

Front-end

Back-end

Middleware

End users

Programmers,networkadministrators

Users, programmers,networkadministrators

Database management systemsNetwork securityApplication integrity backupsDisaster recovery

User interfacesApplication development toolsDocument managementData access

Smooth communication betweenthe client and server

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The Growth in Client/Server Computing

The ubiquity of PCs

The interest in corporate downsizing

The high cost of running and maintaining mainframes

The rapid growth in client/server computing can be traced to three powerful forces:

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Client/Server Database Applications

Graphical user interface

Program to access data

Data

Database management system

Client Server

Network

Client’s requests are sent using structured query language (SQL)

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Client/Server Database Applications (cont.)

Database Transaction processing

An exchange between two entities

E-mail

Various client/server applications:

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Advantages and Disadvantages of Client/Server Systems

Advantages

Data are readily accessible to decision makers

Reduced operating costs

Reduced system development and maintenance time

Increased organizational responsiveness

Disadvantages

Resistance to change

High training costs

Extensive planning required

Inadequate standards

Susceptible to security violations

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Advantages of Client/Server Systems

Data Are Readily Accessible to Decision Makers Timely information can often

translate into tangible benefits, such as increased profits or reduced operating costs; and intangible benefits, such as greater customer satisfaction.

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Advantages of Client/Server Systems (cont.)

Reduced Operating Costs In the long run, the cost of

information processing may be cheaper for client/server systems than for mainframe systems, thereby lowering overall operating costs.

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Advantages of Client/Server Systems (cont.)

Reduced System Development and Maintenance Time With proper planning and the

necessary expertise, developers can create client/server systems more quickly and efficiently than mainframe applications.

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Advantages of Client/Server Systems (cont.)

Increased Organizational Responsiveness Designing a client/server system

often compels managers and employees to search for more efficient, more effective business practices.

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Disadvantages of Client/Server Systems

Resistance to Change The transition from a mainframe

environment to a client/server environment is fraught with obstacles. It is clear that the knowledge, experience, and expertise guiding these mainframe and client/server technologies are quite different.

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Disadvantages of Client/Server Systems (cont.)

High Training Costs Users need extensive training to

successfully use and manage client/server environments. Because these systems often change the dynamics of the business environment, training must be comprehensive and include both the business and the technology side.

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Disadvantages of Client/Server Systems (cont.)

Extensive Planning Required A business must plan carefully and

develop a strategic plan for a client/server system. Without a plan, the system becomes an ad hoc collection of systems that don’t integrate information and streamline business processes.

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Disadvantages of Client/Server Systems (cont.)

Inadequate Standards Like any other new and evolving

technology, client/server systems lack standardization in terms of system management, maintenance, and security, resulting in some reinventing of the wheel.

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Disadvantages of Client/Server Systems (cont.)

Susceptible to Security Violations The security concerns associated with

client/server systems are greater than those associated with other information systems because client/server systems are prone to security violations. The same features that make the client/server flexible, modular, open, and responsive also make it risky and vulnerable.

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Guidelines for Client/Server Success

Know Thy Business and Its Goals A key question at the heart of successful

client/server systems is “Why do we do what we do?”

Plan, Plan, Plan The plan should identify the areas in the

company that will lend themselves well to automation and then specify client/server technologies that will meet those automation needs.

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Guidelines for Client/Server Success (cont.)

Training Is the Key Reengineering almost always precedes the

development of client/server systems. As a result employees are faced not only with a new system but also with a new or a different way of doing business.

Make Sure the Data Has Integrity Data are essential to good decision making.

The best of systems is only as good as the data that go into it.

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Guidelines for Client/Server Success (cont.)

Establish Standards What kind of hardware are we going to use for

servers? What kind of hardware are we going to use for

clients? What software will the company use to establish

communications between clients and servers? What kind of applications will run on the clients?