HHMI 02 Web: Web Info 2

Web Info 2
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Addressing In The Web
We said that we need to "(2) 'call up' another computer, the server running the Web server software, to ask for the information that we want..."

How do we know what to ask for?

To get files from a server on the Web, we need to know

the name of the file (information) -- either by having a page that links to it, or by knowing the name "off hand," and
the name of the server on which it is located -- again, either by having a page that links to it or by knowing off hand what it is.

In particular, suppose we want to get the file from the Web called index.html located on a server called howard.nebrwesleyan.edu...

server/file structure

(All of the files that are served by the server are just ordinary, every-day files that are located in a special directory on the server. We call this a Web Documents directory or folder, as shown to the right -- we'll come back to this in a moment.)

The address of the file is a URL (for Uniform Resource Locator) that tells How to get the file, Where to get it from, and What file to get:
http://howard.../index.html
or, interpreting this in various levels of abstraction, how://where/what
how://server/file
"http" is HyperText Transfer Protocol
the server is just the name of the server (howard.nebrwesleyan.edu), and
the file is just the name of the file (index.html).

Piece o' cake.

Note that for most servers, the filename index.html or index.htm is implied, so that the address
http://howard.../
would be the same thing as that given above. In most cases the trailing "/" is also implied, so that it can also be left off.

Subdirectories
To get the file index.html in the "math" subdirectory of the "classes" directory (see the image above), the URL would be
http://howard.nebrwesleyan.edu/classes/math/index.html
or http://howard.nebrwesleyan.edu/classes/math/
To get to subdirectories in the Web Docs directory, insert them separated by "/ "s. (Did you guess that the ... in the addresses we gave above represented ".nebrwesleyan.edu"? Good. So did I.)

What's a link? It's just somewhere in a page where the person who
wrote the page hid one of the URLs that we've been talking about...

Web documents are just any old files located in a Web Documents directory on a server,
These files are requested by a browser using a URL that specifies how to get the file, and from where (the name of the server), and
A URL also specifies the path (subdirectories) to the file.
A link is just somewhere a reference -- to a URL -- has been embedded in a Web document.

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Gavin's HHMI 02 Web Workshop: Web Info 2
Last Modified: Thu May 30 12:51:16 EDT 2002
Comments to glarose@umich.edu
©2002 Gavin LaRose, UM Math Dept