The Internet Encyclopedia (Volume 3)

P1: c-161

SoftwareDesign WL040/Bidgoli-Vol III-Ch-24 June 23, 2003 16:25 Char Count= 0

WEBSOFTWAREENGINEERINGQUALITYFACTORS 287

Server Side

HTTP Server

CGI programs

Data Base Files

Client Side

Browser

HTML

Forms

Images

Helper

audio

video

User

Figure 1: First-generation Web sites.

among software components with XML (extensible

markup language), and a number of design architectures

for large-scale Web software applications. Figure 2

illustrates a typical configuration for a fourth-generation

Web application.

Most of the software has been moved to a separate

computer, the application server. Large Web sites imple-

ment the application server as a collection of application

servers that operate in parallel. Likewise, Web servers are

often clusters of computers that work together to server

requests from large numbers of users. Application servers

typically interact with one or more database servers, often

running a commercial database. The client–server inter-

action, as before, uses the Internet. The Web servers and

application servers are connected by middleware, which

are packages obtained from software vendors to handle

functions such as communication, data translation, and

process distribution. Middleware is sometimes as simple

as Java Data Base Connectivity (JDBC), whereas other

middleware packages are large and solve complicated

problems. Likewise, the application-database servers of-

ten interact through middleware.

WEB SOFTWARE ENGINEERING

QUALITY FACTORS

Although software engineering researchers, educators,

and practitioners have spent years focusing on develop-

ing processes and technologies to improve software qual-

ity attributes, much of the software industry has had lit-

tle motivation to improve the quality of their software.

Software is often sold with relatively low-quality require-

ments; the combination of user expectations and market

realities has been such that increasing quality usually has

not increased profits. A combination of time-to-market

and marketing strategies has almost always determined

whether traditional software products succeed compet-

itively. As an example, software contractors for govern-

ment agencies are often paid the same regardless of the

quality of the delivered software. Despite the positive im-

pacts of the capability maturity model (Carnegie Mellon

Software Engineering Institute, 2002), many contractors

are still given additional resources to correct problems of

their own making (Tassey, 2002). Commercial software

companies (so-called shrink-wrap vendors) are usually

Application DB

ApplicationServer

Client Server

Client

Client

Application

Server

Client

WebClient

Server

Network Middleware Middleware DBDB

Figure 2: Multitier Web sites.