A URL is effectively the globally-unique address of some resource (document, image, media file, etc.) on the Internet. URLs have three components. The first gives the access method and defins the protocol that the user agent (in the case of the Web a Web Browser) should use to connect to the server. Examples are http, ftp, mailto, file and telnet. The second part is the IP address or Fully Qualified Domain Name of the host that has the resource: for example www.swan.ac.uk. The third part is an address of the resource on the server and this normally takes the form of a Unix-Style file path, e.g.: /engineering/UndergraduateDegrees/. Taken all together, a complete URL looks like: http://www.swan.ac.uk/engineering/UndergraduateDegrees/.

You will be most familiar with URLs that you type into the address bar of your browser, but the target of all links, images, flash-movies, CSS style sheets and JavaScripts that are to be found in a modern web page are also accessed by URLs. In fact the URL is so useful, it can be used (in any of the common forms) as a file name in Java!

See also: URI.

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