A Uniform Resource Locator[3] is an address used to specify the location of a resource on the World Wide Wed. Each URL consists of a protocol specifier, server hostname with optional port number, and a document name. The most commonly used protocol on the web is the Hypertext Transport Protocol, specified with "http". Other protocols such as the Secure HTTP, File Transport Protocol, Network News Transport Protocol, Gopher, and Telnet are specified with "https", "ftp", "nntp", "gopher", and "telnet" respectively.
Prior to the web, it was fairly common for institutions to name specific servers after their primary function. FTP servers were named ftp and SMTP (Electronic mail) servers were named mail. These naming conventions made it easier for users to locate services at a particular organization. This tradition was extended to the web and it is very common to find web servers named "www". It is very likely that a user trying to find information about company "XYZ" will find a web server running on "www.xyz.com". An example URL is shown in Figure 2.3. This is the URL used to access San Diego State University.
