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WWW Everyone
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http://www.ncsa.uiuc.edu:70/demoweb/html-primer.html#A1.3.2.1
The key to a hypertext system is being able to specify where to jump when the
user clicks the mouse. This problem is elegantly solved for the WWW by use of
Uniform Resource Locators, or URLs. A URL is a succinct way of encoding the location
of the remote server, the protocol that the server understands, and the message
necessary to send to the server to obtain the pointed-to document. Consider the
URL given above. URLs always start with the protocol of the server, followed by
a colon, in this case the Web's http:. Other possible protocols are gopher,
telnet, ftp, news, and mailto.
Next comes the address and port of the server, namely //www.ncsa.uiuc.edu:70/.
Addresses start with "//", and have the standard domain-style format. When necessary,
the address is followed by another colon, then a port number. Port 70 is the
default for HTTP, so actually the port is not explicitly required in this example.
(Port numbers are used so that the server knows which internal processes should
respond to the client's request. This is standard TCP/IP networking, not related
to WWW.)
Then comes another /. The rest of the URL is simply a string that is
sent to the server to specify which document is to be delivered. In this particular
case, the file requested is demoweb/html-primer.html, NCSA's primer on
HTML. The optional #A1.3.2.1 instructs the browser to move the cursor
to the position in the document called A1.3.2.1 when it opens the document.
For more about URLs -- a URL: http://www.ncsa.uiuc.edu/demoweb/url-primer.html
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