URL (Uniform Resource Locator)
URL (UNIFORM RESOURCE LOCATOR)
Uniform Resource Locators (URLs), also known as Uniform Resource Identifiers (URIs) or occasionally as Universal Resource Locators, are strings of letters, numbers, and special characters that constitute the addresses of documents, files, electronic mailboxes, images, and other resources in cyberspace. One of the hallmarks of Tim Berners-Lee's invention of the World Wide Web was the ability to make all information on the Internet accessible by a simple click of the mouse, rather than through the tedious process of logging on to various servers and following their own unique interfaces. URLs are the means by which that is accomplished.
The most common use of a URL is to designate an address on the World Wide Web. This address appears in the "Location:" or "Go to:" box of most Web browsers. URLs all follow a similar basic pattern. First, the URL string is prefixed by a code indicating the particular access method for the electronic resource. These schemes include the following.
- Hypertext Transfer Protocol (indicated by the prefix "http:"), the standard method for downloading documents and images on the Web.
- File Transfer Protocol ("ftp:"), used primarily for downloading files from one server to another.
- Electronic mailboxes ("mailto:"), for sending e-mail
- Gopher ("gopher:"), for accessing files on a Gopher server.
- Usenet News ("news:") for referencing Usenet newsgroups.
- The Telnet protocol ("telnet:") for connecting to a remote host's internal system.
- Wide Area Information Servers ("wais:") for accessing a WAIS database.
- Host-Specific File Names ("file:") for retrieving documents from a remote host using a chosen protocol.
- The Prospero Directory Service ("prospero:") for tapping into Prospero resources.
The next section of the string indicates the domain name of the server being accessed. The suffix of this section indicates either what kind of server it is or in what country it's located. For instance, the "com" suffix in the domain name "www.website.com " indicates that the particular file being accessed resides on a commercial server; the suffix "uk" indicates that the server is located in the United Kingdom. The list of such suffixes was growing in the early 2000s as regulators sought to accommodate the expansion of the Web.
Any information that appears after this string simply designates where in the server's hierarchical file structure the particular resource is located—that is, it spells out the path to the file. For instance, a URL—www.website.com/files/webpage.html " indicates that the resource is stored on the "website.com " server in a folder called "files," and that the file "web-page" is an HTML document.
This syntax was defined by the policy document RFC 1738 produced by the Network Working Group of the Internet Engineering Task Force. To locate an Internet resource, the URL must be matched exactly. URLs rendered with flaws will fail to turn up the desired resource. Certain characters are avoided entirely in URLs, since for various reasons they are deemed "unsafe." Spaces, for instance, are always to be avoided, while characters such as angle brackets are discouraged because they are often used to mark out URLs in free text. That is, these characters are used to list URLs in documents, marking the beginning and end of the URL string. To avoid confusion over exactly what should be entered as a URL, these characters are discouraged.
FURTHER READING:
Berners-Lee, T., L. Masinter, M. McCahill, eds. "RFC 1738." Internet Engineering Task Force, December 1994. Available from www.cis.ohio-state.edu.
The World Wide Web Consortium. "Web Naming and Addressing Overview (URIs, URLs)." Cambridge, MA: The World Wide Web Consortium, 1997. Available from www.w3.org.
SEE ALSO: Domain Name; ICANN
URL
is the URL of a starting point for new Web users.