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The WWW is a new way of viewing information -- and a rather different
one. If, for example, you are viewing this paper as a WWW document,
you will view it with a browser, in which case you can immediately
access hypertext links. If you are reading this on paper, you will
see the links indicated in parentheses and in a different font. Keep
in mind that the WWW is constantly evolving. We have tried to pick
stable links, but sites reorganize and sometimes they even move. By
the time you read the printed version of this paper, some WWW links
may have changed.
The World Wide Web
The WWW project has the potential to do for the Internet what
Graphical User Interfaces (GUIs) have done for personal computers --
make the Net useful to end users. The Internet contains vast
resources in many fields of study (not just in computer and technical
information). In the past, finding and using these resources has been
The Web provides consistency: Servers provide information in a
consistent way and clients show information in a consistent way. To
add a further thread of consistency, many users view the Web through
graphical browsers which are like other windows (Microsoft Windows,
Macintosh windows, or X-Windows) applications that they use.
A principal feature of the Web is its links between one document and
another. These links, described in the section on hypertext, allow
you to move from one document to another. Hypertext links can point
to any server connected to the Internet and to any type of file.
These links are what transform the Internet into a web.
A History of the Web
The Web project was started by Tim Berners-Lee at the European
Particle Physics Laboratory (CERN) in Geneva, Switzerland. Tim wanted
to find a way for scientists doing projects at CERN to collaborate
with each other on-line. He thought of hypertext as one possible
method for this collaboration.
Tim started the WWW project at CERN in March 1989. In January 1992,
the first versions of WWW software, known as Hypertext Transfer
Protocol (HTTP), appeared on the Internet. By October 1993, 500 known
HTTP servers were active. When Robelle joined the Internet in June
1994, we were about the 80,000th registered HTTP server. By the end
of 1994, it was estimated that there were over 500,000 HTTP servers.
Attempts to keep track of the number of HTTP servers on the Internet
have not been successful. Programs that try to automatically count
HTTP servers never stop -- new servers are being added constantly.
On-Line versus Batch
This paper is available on the World Wide Web (on-line) or as a paper
document (batch). If you are reading this via Robelle's WWW Service, you
probably already know how to access the on-line version.
Much of the value of the Web lies in its links between one document
and another. When you view this paper with a WWW browser, the links
are hidden from you. When you read the text or paper copy of this
paper, you see the links in parentheses. Because links tend to be
long, they do not format well in the text and paper versions. Since
more than half the effort of writing this paper went into finding and
testing the links, we have left them in the text and printed versions,
despite their distracting appearance. We will describe what the links
mean a little later.
What is Hypertext?
Hypertext provides the links between different documents and different
document types. If you have used Microsoft Windows WinHelp system or
hypercard application, you likely know how to use hypertext. In a
hypertext document, links from one place in the document to another
are included with the text. By selecting a link, you are able to jump
immediately to another part of the document or even to a different
document. In the WWW, links can go not only from one document to
another, but from one computer to another.
The last few years have seen an explosion of information about
client/server computing. For many people, the definition of
client/server is still unclear. We describe it as a method of
distributing applications over one or more computers. A client is one
process that requests services of another process. These processes
can be on different computers or on the same computer. The processes
communicate via a networking protocol.
People often think of client/server computing in terms of local area
networks, PCs with graphical user interface capabilities, and servers
with information that is needed by the PC clients. You do not have to
implement client/server computing this way. It is possible for the
same computer to be both the client and the server. The key point is
that there is a communications protocol that allows two processes
(often on different computers) to request and to respond to demands
The Hypertext Transfer Protocol
When you use a WWW client, it communicates with a WWW server using the
Hypertext Transfer Protocol (HTTP). When you
select a WWW link, the following things happen:
this with traditional terminal/host computing. Users usually logon
(connect) to the server and remain connected until they logoff
(disconnect). An HTTP connection, on the other hand, is made only for
as long as it takes for the server to respond to a request. Once the
request is completed, the client and the server are no longer in
- The client
looks up the hostname and makes a connection with the WWW server.
- The HTTP software on the server responds to the client's request.
- The client and the server close the connection.
WWW clients use the same technique for other protocols. For example,
if you request a directory at an
anonymous FTP site, the WWW client makes an FTP connection, logs
on as an anonymous user, switches to the directory, requests the
directory contents, and then logs off the FTP server. If you then
select a file, the WWW client once again makes an FTP connection, logs
on again, changes directories, downloads the file, and then logs off.
If you use an FTP client to do the same thing, you would normally log
on to the FTP server, change directories several times, and download
one or more files. Only when you were finished would you log off.
The Internet is the world's largest interconnected computer network.
Computers on the Internet communicate using the Internet Protocol (IP)
and the Transmission Control Protocol (TCP). You identify individual
computers by their IP-address. This address is a 32-bit number that
is usually represented by four octets (e.g., 126.96.36.199).
Fortunately, you can usually refer to a computer by its name (e.g., www.robelle.com).
If you can send network packets to one computer on the Internet, you
can send network packets to any computer on the Internet. This
feature is what makes the Internet so powerful; it is also what
concerns system managers. If you can send packets to the Internet, it
follows that anyone can send packets to your computer, even the PC on
Accessing the Internet
If you are reading the text or paper version of this paper, you're
probably wondering "How do I get started on the Internet?" It is much
easier to connect an individual PC and a modem to the Internet than it
is to connect a server like an HP 3000 or HP 9000. We suggest that
you find a local Internet access provider to connect your PC to the
Net. Most access providers include everything you need to log on and
start exploring. In addition, several books on connecting to the
Internet also provide all the software and the telephone numbers of
Internet access providers you need to get started.
Once you're connected to the Internet, you can begin investigating
many of the sites described in this paper. You will also be able to
access and download much of the software needed to create your own WWW
application which, as we discuss further on, can be of help to you,
even if you never plan to connect your servers to the Internet.