Uniform Resource Locators (URLs)

A coherent method of identifying items on the Internet.

Uniform Resource Locators (URLs) are a type of address used on the World Wide Web to identify HTML pages, files, Gopher sites, and other sources of information.

The syntax for URLs is simple. The first part of the URL identifies the type of resource. Some of the more common types are as follows:

http
Specifies a document on a Web server (Hypertext Transport Protocol)
gopher
Used for gopher servers, a text-based information distribution protocol
file
Identifies a file on a computer system. This replaces the old ftp file retrieval method, which was difficult to use and prone to breakdown
telnet
This type is the "computer connection" type. What you will usually get is a separate window in which you are connected to the computer that you specify in the second part of the address.

The second part of the URL is the name of the computer that has the information you desire. Note that for a given name, there is (as of today) one computer, but that one computer may have several different names or aliases. It would actually be a substantial improvement on the Web if one name could refer to any of several computers, especially for search tools, where any single computer often gets bogged down with searches.

Computer names are generally formed by taking the name of the computer, the name of the institution, and the type of the institution and concatenating them with periods in between each of the parts. So, for example, Messiah College's Web server is www.messiah.edu (actually, almost all Web servers are called www).

This second part of the URL sometimes has a port number as part of it. You can think of a port number as a P.O. box.

The third part of the URL, which may or may not be present, is the name of the file (or html page, or Gopher directory).

Some more or less invented URLs follow:

http://www.messiah.edu:5080/
gopher://stis.nsf.gov/
file://ophelia.lcl.cmu.edu/~aist/resume.html

Notice that there is some punctuation present besides the periods in the computer names and file names. You must always include a colon and two forward slashes between the first and second parts of the URL. If there is a port number, a colon must separate it from the computer name. Finally, a forward slash separates the second part of the URL from the third part. The Web is terribly picky about exact punctuation, but the good news is that you don't have to learn a different syntax for each new computer. The Web, like nearly all that is computerized, does what you say, not what you mean.