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protocols

Of course if I had insisted everyone use HTTP, this would also have been against the principle of minimal constraint. If the Web were to be universal, it should be as unconstraining as possible. Unlike the NeXT computer, the Web would come as a set of ideas that could be adopted individually in combination with existing or future parts. Though HTTP was going to be faster, who was I to say that people should give up the huge archives of data accessible from FTP servers?

The key to resolving this was the design of the URI. It is the most fundamental innovation of the Web, because it is the one specification that every Web program, client or server, anywhere uses when any link is followed. Once a document had a URI, it could be posted on a server and found by a browser.

Hidden behind a highlighted word that denotes a hypertext link is the destination document's URI, which tells the browser where to go to find the document. A URI address has distinct parts, a bit like the five-digit zip code used by the U.S. postal system. The first three numbers in a zip code designate a certain geographic region—a town, or part of a city or county. The next two numbers define a very specific part of that region—say, a few square blocks in a city. This gets the mail to a local post office. Carriers from there use the street name or box number to finish the routing.

Slashes are used in a URI address to delineate its parts. The first few letters in the URI tells the browser which protocol to use to look up the document, whether HTTP or FTP or one of a small set of others. In the address http://www.foobar.com/doc1, the www.foobar.com identifies the actual computer server where these documents exist. The doc1 is a specific document on the www.foobar.com server (there might be hundreds, each with a different name after the single slash). The letters before the double slash signify the communications protocol this server uses.

The big difference between the URI and postal schemes, however, is that while there is some big table somewhere of all