The Internet Encyclopedia (Volume 3)

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770 WEBSITEDESIGN

Figure 2: Block diagram of a Web site interaction

with client-side scripting.

There are several client-side scripting languages, the

most common one being JavaScript, an object-oriented

language originally developed by Netscape. It is now a sta-

ndardized language, defined by the international industry

group European Computer Manufacturers Association,

and called ECMAScript (European Computer Manufac-

turers Association, 1999). Netscape continues to use the

term JavaScript, however, and Microsoft calls its imple-

mentation of ECMAScript for Windows browsers JScript.

The other major scripting language is Microsoft’s VB-

Script, short for Visual Basic Scripting Edition, which is

available only for Windows platforms (Champeon, 2001).

Regardless of the language, client-side scripts rely on a

standard programming interface, defined by the W3C and

called the Document Object Model (DOM), to dynamically

access and update the content, structure, and style of Web

documents (World Wide Web Consortium, 1998).

Cascading style sheets (CSS) is another W3C language

standard that allows styles (e.g., fonts, colors, and spac-

ing) to be associated with HTML documents. Any specific

HTML tag or group of HTML tags can be modified. It is

a language, separate from HTML, that expresses style in

common desktop publishing terminology. The combina-

tion of HTML, CSS, and DOM client-side scripts is often

referred to as dynamic HTML (Lie & Bos, 1999).

Client-side scripting is used primarily for dynamic user

interface elements, such as pull-down menus and ani-

mated buttons. The advantage of using client-side scripts

instead of server-side scripts for such elements is that

the execution is more immediate. Since the script, once

loaded from the server, is being executed by the browser

directly on the user’s computer, there are no delays asso-

ciated with the network or the server load. This makes the

user interface responsive and similar to standard platform

applications.

One of the disadvantages is that client-side scripting

languages are usually more limited in functionality than

server-side languages, so that complex processing is not

possible. Such limitations are by design, for security rea-

sons, and are not usually apparent for simple user inter-

face programming.

Users may also specifically choose not to allow client-

side scripts to execute on their computers, resulting in a

partial or complete reduction in functionality and usabil-

ity of a Web site. In general, it is recommended that a site

incorporate user interface scripting only sparingly, and

always with clear and functional alternatives.

Finally, because client-side programs, whether embed-

ded or stored separately, must necessarily be accessible

and viewable by the Web browser, they are also ulti-

mately viewable by the user. This may not be desirable for

Figure 3: Block diagram of a Web site interaction with

server-side scripting.

commercial Web applications, where the programming

logic can be considered intellectual property.

Since client-side scripts are embedded in HTML pages,

any tool that creates and edits HTML pages can also be

used to create the scripts. The only requirement is that

the client browser support the particular scripting lan-

guage. Most modern browsers support some variation of

Javascript/ECMAScript/JScript, whereas a smaller subset

support VBScript.

Server Side

Figure 3 shows the basic architecture for a server-side dy-

namic site. Scripts are still stored in HTML documents on

the server’s file system, but are now executed on the server,

with only the program results and output being sent to the

client browser, along with the rest of the HTML page. To

the client browser, the HTTP response is a normal static

HTML Web page. Scripts are embedded in HTML docu-

ments using special HTML-like tags, or templates, whose

syntax depends on the particular server-side scripting lan-

guage (Weissinger, 2000).

There are several common server-side scripting lan-

guages, including PHP, Active Server Pages (ASP), and

Java Server Pages (JSP). The common gateway interface

(CGI) is also a server-side scripting mechanism, whereby

neither the Web content nor the programming logic is

stored in an HTML file. A separate program, stored in the

file system, dynamically generates the content. The Web

server forwards HTTP request information from the client

browser to the program using the CGI interface. The

program processes any relevant user input, generates an

HTML Web document and returns the dynamic content

to the browser via the Web server and the CGI interface.

This process is illustrated in Figure 4.

Server-side scripting is used primarily for complex and

time-consuming programming logic tasks, where imme-

diacy of response is not as critical as with user interface

elements. The advantage of using server-side scripts is the

freedom and computational power that is available on the

Figure 4: Block diagram of a Web site interaction

with common gateway interface scripting.