From Wikipedia, the free encyclopedia.
A Uniform Resource Locator, URL (pronounced as "earl" (SAMPA: [@rl]) or spelled out), or web address, is a standardized address for some resource (such as a document or image) on the Internet. First created by Tim Berners-Lee for use on the World Wide Web, the currently used forms are detailed by IETF standard RFC 2396 (1998).
The URL was a fundamental innovation in creating the World Wide Web It combines into one simple address the four basic items of information necessary to find a document anywhere on the Internet:
- The protocol to use to communicate with that machine
- The machine or domain name to go to
- An open network port on the target machine connected to some service
- The path or file name on that machine
- http specifies which protocol to use.
- //www.wikipedia.org specifies the domain name to contact.
- 80 specifies the network port number of the remote machine. Under most circumstances, this portion may be omitted entirely. In the case of the http protocol the default value is 80.
- /wiki is the request path on the specified system.
Note that in www.wikipedia.org/wiki/Train the hierarchical order of the five elements is org - wikipedia - www - wiki - Train, i.e. before the first slash from right to left, then the rest from left to right.
HTTP URLs can also contain additional elements, like a query string (placed after the path and separated from it by a question mark (?)) containing information from a HTML form with method=get, or a name tag (placed after the path and separated from it by a sharp mark (#)) giving the location within a hypertext page to display. FTP URLs often contain a port number.
http://www.wikipedia.org/w/wiki.phtml?title=Train&action=history http://www.wikipedia.org/wiki/Train#Model_railwaysURLs are one type of URI.
The term URL is also used outside the context of the World Wide Web. Database servers specify URLs as a parameter to make connections to it. Similarly any Client-Server application following a particular protocol may specify a URL format as part of its communication process.
Example of a database URL :
jdbc:datadirect:oracle://myserver:1521;sid=testdbIf a webpage is uniquely defined by a URL it can be linked to (see also deep linking). This is not always the case, e.g. a menu option may change the contents of a frame within the page, without this new combination having its own URL. A webpage may also depend on temporarily stored information. If the webpage or frame has its own URL, this is not always obvious for someone who wants to link to it: the URL of a frame is not shown in the address bar of the browser, and a page without address bar may have been produced. The URL may be derivable from the source code and/or "properties" of various components of the page.
Apart from the purpose of linking to a page or page component, one may want to know the URL to show the component alone, and/or to lift restrictions such as a browser window without toolbars, and/or of a small non-adjustable size.
For Wikipedia, see Wikipedia:URLs.