Information Technology Reference
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site. This protocol requests a computer called the
web server
at the remote site to
upload the requested web page to the user's browser for viewing (
Fig. 11.9
).
In November 1990, Nicola Pellow, a student visiting CERN from Leicester
Polytechnic (now De Montfort University) in England wrote a web browser
called a
line-mode browser
that worked on almost all computer terminals. Her
browser enabled Berners-Lee's small team to release the World Wide Web
program to people at CERN who had NeXT computers in March 1991. One
of the key converts to the web was Paul Kunz, a visitor to CERN from the
Stanford Linear Accelerator Center (SLAC) in Palo Alto, California. He was
also a NeXT enthusiast. After Kunz returned to the United States, he worked
with Louise Addis, the SLAC librarian, and their colleague Terry Hung to
make SLAC's catalog of online documents accessible using the web. Berners-
Lee announced this offering on 13 December 1991. The first web server in
the United States, the SLAC home page, slac.html, was created six months
later and was the first web server outside CERN (
Fig. 11.10
).
To evangelize the World Wide Web, Berners-Lee and Cailliau wrote up
their work as a paper for the major Hypertext Conference sponsored by the
Association for Computing Machinery that was scheduled to take place in San
Antonio, Texas, in December 1991. It is part of the folklore of computer sci-
ence that their paper was rejected! In spite of this rejection, they asked for
permission to give a demonstration. This was not easy to arrange because,
at that time, the conference provided no Internet connectivity to attendees.
Cailliau had to call up a local university and arrange to use their dial-in service.
As Berners-Lee says:
<HTML>
<TITLE>
A sample HTML instance
</TITLE>
<H1>
An Example of Structure
</H1>
Here's a typical paragraph.
<P>
<UL>
<LI>
Item one has an
<A NAME="anchor">
anchor
</A>
<LI>
Here's item two.
</UL>
</HTML>
Fig. 11.7. Example of a simple text with
bracketed codes indicating the docu-
ment elements in HTML from the June
1993 specification.
We were the only people at the entire conference doing any kind of
connectivity. . . . At the same conference two years later … every project on
display would have something to do with the Web.
14
The value of the web increased rapidly as more sites put up web servers and
made their content available to other computers using the HTTP protocol. The
real breakthrough happened when images started to appear on web pages
(
Fig. 11.11
). In the summer of 1992, David Williams suggested that Berners-Lee
should take sabbatical leave from CERN to visit the United States. Berners-Lee
spent time at MIT (
B.11.6
) on the East Coast and at Xerox PARC on the West
Coast promoting his ideas. While he was in the San Francisco area, he visited
Paul Kunz and Louise Addis at SLAC but also took the time to pay homage
to another Bay Area resident, Ted Nelson, who was the original inventor of
hypertext.
By the end of 1992, the CERN team had a list of about thirty web servers,
mainly in Europe, but also a handful based in the United States. NCSA at the
University of Illinois, Urbana, was one of these U.S. sites. Traffic to the first
web server at CERN was growing rapidly, with the number of daily
hits
- page
views - doubling every three to four months. We can now see the relevance of
“Error 404” in the title of this section. The error 404 message appears whenever
a web client follows a link to a server but either the server is no longer there or
the server is unable to find the requested page. The user typically receives an
error message saying “Error 404 - Page Not Found” when attempting to follow
such a broken or dead link. Berners-Lee's great insight was to realize that such
Fig. 11.8. Screenshot from the first text-
based browser developed at CERN.
Server
Browser
User clicks a link
TCP connection request
TCP connection port
HTTP page request
Accept TCP
request
Accept TCP
connection
Accept HTTP
request
Acknowledge HTTP request
Wait for the
web page
Data sent to the client
Accept data
Acknowledge data
Te rminate TCP connection
Fig. 11.9. The HTTP is a sequence-
response procedure. The figure illus-
trates the sequence of messages between
the browser and the server when the
user clicks on a hyperlink.
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