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URL - pronounced either "Earl" or more properly letter by letter,
is the address where you find a web page.
Here are some typical examples:
- http://ctl.unbc.ca
- http://ctl.unbc.ca/ptheory/a1ptnav.html
- http://ctl.unbc.ca/row/v1n4/gallery/ewen/ewenTAB1.html
Each has four parts, color coded to match the examples above:
protocol://domain.name/path/file.ext
The parts are described below.
Protocol
http (hypertext transfer) is by far the most common protocol these
days. So much so that it is usually assumed by default if you
leave this part out
domain.name
The domain name describes a machine or virtual machine. At any given
time, a single domain name will (or should) map (or connect with) exactly
one machine. Sometimes more than one domain name will map to the same
machine. That is how multiple domain names can be hosted on one physical
machine. The domain name is translated to an IP (Internet protocol)
address which is a series of numbers separated by periods by a special
machine called a domain name server, or DNS.
Path
The use of the term "path" here is the same as it is in file
management. It lists the directories from the root of a file system
to the desired one. The slashes go / and not \ in URLs and the root
is not the physical root directory of a disk drive but a virtual root
directory. It is the root, that is, but only from the perspective of
world wide web software. Anything above this "web server virtual
root" visitors on the web cannot see and should not care about.
So the virtual root is "as good as" a root directory for web
access purposes.
File.ext
This is the name of the file. If none is specified, then by default
most servers assume you want the one named index.htm or index.html or
sometimes home.htm even. If you want another file in the directory targeted,
you have to specify it. The usual extension is .htm or .html but you
will encounter others.
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