The Internet Encyclopedia (Volume 3)

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DYNAMICSITES 769

generates new data. It drives the interaction between the

Web site and the user and is the glue that binds the content

and its presentation. To be useful, it needs to access the

content as well as its presentation information and han-

dle user input accordingly. Logic is usually implemented

as small programs, or scripts, that are executed on the

Web server or the user’s browser. These scripts can be

stored within the HTML page, along with the presentation

and content, or separately as distinct program files that

are associated with the content. There are several stan-

dard programming languages that can be used in writing

scripts.

Separation of Components

With the existence of a variety of technologies, protocols,

and standards, Web development is remarkably flexible,

and there are often multiple ways of accomplishing the

same task. This is both an asset and a liability, as while

developers are free to choose their own techniques, it is

very easy to create sloppy or undisciplined documents and

code. In regular application development, it is important

to adhere to sound software engineering techniques to

manage a code base for future enhancements and simul-

taneous development efforts. The flexibility of Web deve-

lopment makes such good techniques even more critical.

Until very recently, there was a great deal of overlap,

in terms of storage and implementation, of the three Web

site components mentioned above. This led, for example,

to Web pages that contained all three components in a

single, often unmanageable, HTML file. As Web site de-

velopment has matured, the principle of Web site com-

ponent separation has become widely encouraged, if not

accepted, and it is the central theme of this chapter.

IMPLEMENTATION ISSUES

The World Wide Web (WWW) is a series of client/server

interactions, where the client is the user’s Web browser,

and the server is a particular Web site. The WWW Con-

sortium (W3C) defines the hypertext markup language

(HTML) and the hypertext transfer protocol (HTTP) as

the standard mechanisms by which content is published

and delivered on the Web, respectively.

In essence, the local Web browser initiates HTTP re-

quests to the remote Web server, based on user input.

The Web server retrieves the particular content specified

by the requests and transmits it back to the browser as

an HTTP response. The Web browser then interprets the

response and renders the received HTML content into a

user-viewable Web page.

Web site implementations can be classified by the level

of interactivity and the way content is stored, retrieved,

and displayed.

Static Sites

Static sites are the simplest type of Web sites, with the

content statically stored in HTML files, which are simple

text files. Updating the Web site requires manually chang-

ing individual HTML text files. While this type of site was

prevalent in the beginning, most sites, especially commer-

cial ones, have come to incorporate at least some degree

Figure 1: Block diagram of a client/server archi-

tecture with a static Web site.

of dynamic behavior, and users have come to expect some

interactivity.

Figure 1 shows the basic client–server interaction for a

static Web site. The client browser makes an HTTP request

to a Web server. The URL specifies the particular Web

server and page. The Web server retrieves the requested

Web page, which is an HTML file, from the file system and

sends it back to the client through the HTTP response.

This very basic interaction between browser and server

is the basis for more complex, dynamic interactions. This

type is static because the Web page content is straight

HTML, statically stored on disk, with no mechanism to

change the contents. The Web server here serves solely as

a file transfer program.

Developing static sites requires very few tools. All that

is required, besides the Web server and browser, is a text

editor application. The simplest text editor can be used to

manually create HTML files. Complex, graphical HTML

editors can make the task almost trivial by automatically

generating HTML files and behaving similarly to word

processors, with WYSIWYG (what you see is what you

get) interfaces. Creating graphics and images for static

Web sites is also straightforward, requiring any typical

paint or drawing program.

DYNAMIC SITES

Dynamic sites share the same basic architecture as static

ones, but with the addition of programming logic. The two

major types of dynamic sites reflect the place of execution

of the scripts. Client-side scripting involves embedding ac-

tual source code in HTML, which is executed by the client

browser in the context of the user’s computer. Server-side

scripts, on the other hand, are executed on the Web server.

While the following discussion examines both types sep-

arately, in an actual Web site both types can and often do

exist simultaneously.

Client Side

Figure 2 shows the basic architecture for a dynamic site

with client-side scripting. Scripts are embedded within

HTML documents with the <script> </script> tags or

stored in separate documents on the server’s file system.

Scripts are transmitted, without execution, to the client

browser along with the rest of the HTML page. When

the client browser renders the HTML page, it also in-

terprets and executes the client script. An example of a

client-side script is the functionality that causes a user

interface element, such as a menu, to provide visual feed-

back when the user moves the mouse pointer over a menu

option.