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URL (Uniform Resource Locator)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

Most people are familiar with URLs. They are the addresses you type in a Web browser Address field that start with http://, followed by the name of a Web site. URLs also refer to addresses used with other Internet protocols, such FTP, Gopher, NNTP (Network News Transport Protocol), Telnet, and WAIS (Wide Area Information Servers), among others. URLs are instances of a broader class of identifiers known as Uniform Resource Identifiers (URIs). See "URI (Uniform Resource Identifier)" for more information.

A resource is an object on the Internet or an intranet that resides on a host system. Objects include directories and an assortment of file types. A URL is the address of an object, a pointer to its location on a server/directory in a particular domain. According to RFC 1738 (Uniform Resource Locators, December 1994), the syntax for a URL is as follows:


The scheme portion identifies a particular protocol such as HTTP, FTP, and so on. The scheme-dependent-information identifies a domain, a server and/or directory, and a particular file. For example, the following address identifies the document security.html in the papers directory at the NTResearch Web site:

One of the downsides of URLs is that they specifically identify a particular path to a file on a particular host. If you embed such a URL in a document and the location of the file changes, then you need to update the URL in the document. This is impractical for some documents, such as those that include bibliographic references and are stored for years. Uniform Resource Names (URNs) provide a way to overcome this problem by providing persistent, location- independent identifiers for Internet resources. See "URN (Uniform Resource Name)" for more information.

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