it-e-24 Understanding the World Wide Web

it-e-24 Understanding the World Wide Web

The World Wide Web is a system of Internet servers that supports hypertext to access
several Internet protocols on single interface. The World Wide Web is often abbreviated as the
Web or WWW.
The World Wide Web was developed in 1989 by Tim Berners-Lee of the European Particle
Physics Lab (CERN) in Switzerland. The initial purpose of the Web was to use networked
hypertext to facilitate communication among its members, who were located in several counties.
Word was soon spread beyond CERN, and a rapid growth in the number of both developers and
users ensued. In addition to hypertext, the Web began to incorporate graphics, video and sound.
The use of the Web has now reached global proportions.

Almost every protocol type available on the Internet is accessible on the Web. Internet

protocols are sets of rules that allow for intermachine communication on the Internet. The
following major protocols are accessible on the Web:
E-mail (Simple Mail Transport Protocol or SMTP): Distributes electronic messages and files
to one or more electronic mailboxes
Telnet (Telnet Protocol): Facilitates login to a computer host to execute commands
FTP (File Transfer Protocol): Transfers text or binary files between an FTP server and client
Usenet (Network News Transfer Protocol or NNTP): Distributes Usenet news articles
derived from topical discussions on newsgroups
HTTP (HyperText Transfer Protocol): Transmits hypertext over networks. This is the
protocol of the WWW.
Many other protocols are available on the Web. To name just one example, the Voice over
Internet Protocol (VoIP) allows users to place a telephone call over the Web.
The World Wide Web provides a single interface for accessing all these protocols. This creates
a convenient and user-friendly environment. It is no longer necessary to be conversant in these
protocols within separate command-level environments. The Web gathers together these protocols
into a single system. Because of this feature and because of the Web's ability to work with
multimedia and advanced programming languages, the World Wide Web is the fastest-growing
component of the Internet.
The operation of the Web relies primarily on hypertext as its means of information retrieval.
HyperText is a document containing words that connect to other documents. These words are called
links and are selectable by the user. A single hypertext document can contain links to many
documents. In the context of the Web, words or graphics may serve as links to other documents,
images, video and sound. Links may or may not follow a logical path, as each connection is
programmed by the creator of the source document. Overall, the WWW contains a complex virtual
Web of connections among a vast number of documents, graphics, videos and sounds.
Producing hypertext for the Web is accomplished by creating documents with a language
called HyperText Markup Language, or HTML. With HTML, tags are placed within the text to
accomplish document formatting, visual features such as font size, italics and bold, and the
creation of hypertext links. Graphics may also be incorporated into an HTML document. HTML
is an evolving language, with new tags being added as each upgrade of the language is developed
and released. The World Wide Web Consortium, led by Tim Berners-Lee, coordinates the efforts
of standardizing HTML.
The World Wide Web consists of files called pages or Web pages, containing information
and links to resources throughout the Internet.
Web pages can be created by user activity. For example, if you visit a Web search engine
and enter keywords on the topic of your choice, a page will be created containing the results of

your search. In fact, an increasing amount of information found on the Web today is served from
databases, creating temporary Web pages "on the fly" in response to user queries. Access to Web
pages may be accomplished by:
Entering an Internet address and retrieving a page directly.
Browsing through pages and selecting links to move from one page to another.
Searching through subject directories linked to organized collections of Web pages.
Entering a search statement at a search engine to retrieve pages on the topic of your
choice.
Today's World Wide Web presents an ever-diversified experience of multimedia, programming
languages and real-time communication. There is no question that it is a challenge to keep up with the
rapid pace of developments. The following presents a brief description of some of the more important
trends to watch.
The Web has become a broadcast medium. It is possible to listen to audio and video over the
Web both pre-recorded and live. For example, you can visit the sites of various news organizations
and view the same videos shown on the nightly television news. Several plug-ins are available for
viewing these videos. For example, Apple's Quick Time Player downloads files with the .mov
extension and displayed these as "movies" in a small window on your computer screen. Quick Time
files can be quite large, and it may take patience to wait for the entire movie to download into your
computer before you can view it.
The problem if slow download times has been answered by a revolutionary development in
multimedia capability: Streaming media. In this case, audio or video files are played as they are
downloading or streaming into your computer. Only a small wait, called buffering, is necessary
before the file begins to play. The RealPlayer plug-in plays streaming audio and video files.
Extensive files such as interviews, speeches and hearings work very well with the RealPlayer.
The RealPlayer is also ideal for the broadcast of real-time events. These may include press
conferences, live radio and television broadcasts, concerts, etc. The Windows Media Player is
another streaming media player. Many sites offer the option to use one player or the other. A list
of sites that make use of these programs is available on the page, Multimedia on the Web.
Shockwave presents another multimedia experience. Shockwave allows for the creation and
implementation of an entire multimedia display combining graphics, animation and sound.
Sound files, including music, may also be heard on the Web. It is not uncommon to visit a
Web page and hear background music. Sound files are also available for downloading
independent of Web page visits. Sound files of many types are supported by the Web with the
appropriate plug-ins. The MP3 file format, and the choice of supporting plug-ins, is the latest
music trend to sweep the Web. The famous Napster site allows for the exchange of MP3 files.
Live cams are anther aspect of the multimedia experience available on the Web. Live cams
are video cameras that send their data in real time to a Web server. These cams may appear in all

kinds of locations, both serious and whimsical: an office, on top of a building, a scenic locale, a
special event, and so on.
The use of existing and new programming languages has extended the capabilities of the
Web. What follows is a basic guide to a group of the more common languages and functions in
use on the Web today.
CGI, Active Server Pages: CGI (Common Gateway Interface) refers to a specification by
which programs can communicate with a Web server. A CGI program, or script, is any program
designed to accept and return data that conforms to the CGI specification. The program can be
written in any programming language, including C, Perl, and Visual Basic Script. A common use
for a CGI script is to process an interactive form on a Web page. For example, you might fill out
a form ordering a book through Interlibrary Loan. The script processes your information and
sends it to a designated e-mail address in the Interlibrary Loan department.
Anther type of dynamically generated Web page is called Active Server Pages (ASP).
Developed by Microsoft, ASPs are HTML pages that include scripting and create interactive
Web server applications. The scripts run on the server, rather than on the Web browser, to
generate the HTML pages sent to browsers. Visual Basic and JScript (a subset of JavaScript) are
often used for the scripting. ASPs end in the file extension .asp.
Java/Java Applets: Java is probably the most famous of the programming languages of the
Web. Java is an object-oriented programming language similar to C++. Developed by Sun
Microsystems, the aim of Java is to create programs that will be platform independent. The Java
motto is, "Write once, run anywhere." A perfect Java program should work equally well on a PC,
Macintosh, Unix, and so on, without any additional programming. This goal has yet to be
realized. Java can be used to write applications for both Web and non-Web use.
Web-based Java applications are usually in the form of Java applets. These are small Java
programs called from an HTML page that can be downloaded from a Web server and run on a
Java-compatible Web browser. A few examples include live newsfeeds, moving images with
sound, calculators, charts and spreadsheets, and interactive visual displays. Java applets can tend
to load slowly, but programming improvements should lead to a shortened loading time.
JavaScript/JScript: JavaScript is a programming language created by Netscape Communications.
Small programs written in this language are embedded within an HTML page, or called externally
from the page, to enhance the page's the functionality. Examples of JavaScript include moving tickers,
drop-down menus, real-time calendars and clocks, and mouse-over interactions. JScript is a similar
language developed by Microsoft and works with the company's Internet Explorer browser.
VRML: VRML (Virtual Reality Modeling Language) allows for the creation of three-dimensional
words. These may be linked from Web pages and displayed with a VRML viewer. Netscape
Communicator comes with the Cosmo viewer for experiencing these three-dimensional worlds. One of
the most interesting aspects of VRML is the option to "enter" the world and control your movements
within the world.
XML: XML (eXtensible Markup Language) is a Web page creation language that enables

designers to create their own customized tags to provide functionality not available with HTML.
XML is a language of data structure and exchange, and allows developers to separate form from
content. At present, this language is little used as Web browsers are only beginning to support it.
In May 1999, however, the W3 Consortium announced that HTML 4.0 has been recast as an
XML application called XHTML. This move will have a significant impact on the future of both
XML and HTML.
Text, audio and video communication can occur in real time on the Web. This capability
allows people to conference and collaborate in real time. In general, the faster the Internet
connection, the more successful the experience.
At its simplest, chat programs allow multiple users to type to each other in real time.
Internet Relay Chat and America Online's Instant Messenger are prime examples of this type of
program. The development of a messaging protocol is underway. Such a protocol would allow
for the expansion of this capability throughout the Internet.
More enhanced real-time communication offers an audio and/or video component. CU-See
Me is one of the most popular software programs of this type. Even more elaborate are programs
that allow for true real-time collaboration. Microsoft's NetMeeting and Netscape's Conference
(available with Communicator) are good examples of this.
Featured collaboration tools include:
audio: conduct a telephone conversation on the Web;
video: view your audience;
file transfer: send files back and forth among participants;
chat: type in real time;
whiteboard: draw, mark up, and save images on a shared window or board.
document/application sharing: view and use a program on another's desktop machine.
collaborative Web browsing: visit Web pages together.
Currently no standard exists that will work among all conferencing programs.
Push: Push refers to a technology that sends data to a program without the program's request.
This is the opposite of the typical "pull" of the Web, in which the user clicks on a link to request
a file from a server. With push, the data is sent automatically. Content is sent through a "channel".
The early Web-based implementation of push was commercial. Push can also be used to deliver
software upgrades to a desktop machine.

1, facilitate  [fə'siliteit]
v. 帮助,使...容易,促进
2, proportions  [prə'pɔ:ʃəns]
n. 比例;大小(proportion的复数形式)
3, retrieval  [ri'tri:vəl]
n. 取回,恢复,修补
4, diversified  [dai'və:sifaid, di-]
adj. 多样化的;各种的
v. 使…多样化(diversify的过去分词)
5, whimsical  ['(h)wimzikəl]
a. 心情浮动的,反覆无常的,古怪的
6, conduct  ['kɔndʌkt, -dəkt]
n. 行为,举动,品行
vt. 引导,指挥,管理
vt. 导电,传热
7, commercial  [kə'mə:ʃəl]
a. 商业的
n. 商业广告


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