Uniform Resource Locator

uniform resource locator

[‚yü·nə‚fȯrm ri‚sȯrs ′lō·kād·ər] (computer science) The unique Internet address assigned to a Web document or resource by which it can be accessed by all Web browsers. The first part of the address specifies the applicable Internet protocol, for example, http or ftp; the second part provides the IP address or domain name of the location. Abbreviated URL.

Uniform Resource Locator

(World-Wide Web)(URL, previously "Universal") A standardway of specifying the location of an object, typically a web page, on the Internet. Other types of object are describedbelow. URLs are the form of address used on the World-Wide Web. They are used in HTML documents to specify the targetof a hyperlink which is often another HTML document(possibly stored on another computer).

Here are some example URLs:

http://w3.org/default.htmlhttp://acme.co.uk:8080/images/map.gifhttp://foldoc.org/?Uniform+Resource+Locatorhttp://w3.org/default.html#Introductionftp://wuarchive.wustl.edu/mirrors/msdos/graphics/gifkit.zipftp://spy:secret@ftp.acme.com/pub/topsecret/weapon.tgzmailto:fred@doc.ic.ac.uknews:alt.hypertexttelnet://dra.com

The part before the first colon specifies the access scheme orprotocol. Commonly implemented schemes include: ftp,http (World-Wide Web), gopher or WAIS. The "file"scheme should only be used to refer to a file on the samehost. Other less commonly used schemes include news,telnet or mailto (e-mail).

The part after the colon is interpreted according to theaccess scheme. In general, two slashes after the colonintroduce a hostname (host:port is also valid, or for FTPuser:passwd@host or user@host). The port number is usuallyomitted and defaults to the standard port for the scheme,e.g. port 80 for HTTP.

For an HTTP or FTP URL the next part is a pathname which isusually related to the pathname of a file on the server. Thefile can contain any type of data but only certain types areinterpreted directly by most browsers. These include HTMLand images in gif or jpeg format. The file's type isgiven by a MIME type in the HTTP headers returned by theserver, e.g. "text/html", "image/gif", and is usually alsoindicated by its filename extension. A file whose type isnot recognised directly by the browser may be passed to anexternal "viewer" application, e.g. a sound player.

The last (optional) part of the URL may be a query stringpreceded by "?" or a "fragment identifier" preceded by "#".The later indicates a particular position within the specifieddocument.

Only alphanumerics, reserved characters (:/?#"<>%+) used fortheir reserved purposes and "$", "-", "_", ".", "&", "+" aresafe and may be transmitted unencoded. Other characters areencoded as a "%" followed by two hexadecimal digits. Spacemay also be encoded as "+". Standard SGML "&<name>;"character entity encodings (e.g. "é") are also acceptedwhen URLs are embedded in HTML. The terminating semicolon maybe omitted if &<name> is followed by a non-letter character.

The authoritative W3C URL specification.

uniform resource locator