Uniform Resource Locator (URL) formerly known as Universal Resource Locator, is a technical,
Web-related term used in two distinct meanings:In popular usage, many technical documents, it is a
synonym for
Uniform Resource Identifier (URI);Strictly, the idea of a uniform syntax for global identifiers of network-retrievable documents was the core idea of the World Wide Web. In the early times, these identifiers were variously called "document names", "Web addresses" and "Uniform Resource Locators". These names were misleading, however, because not all identifiers were locators, and even for those that were, this was not their defining characteristic. Nevertheless, by the time the RFC 1630 formally defined the term "URI" as a generic term best suited to the concept, the term "URL" had gained widespread popularity, which has continued to this day.
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<
World-Wide Web> (URL, previously "Universal") A
standard way of specifying the location of an object, typically a
web page, on the
Internet. Other types of object are described below. URLs are the form of address used on the
World-Wide Web. They are used in
HTML documents to specify the target of a
hyperlink which is often another HTML document (possibly stored on another computer).
Here are some example URLs:
http://www.w3.org/default.html http://www.acme.co.uk:8080/images/map.gif http://www.foldoc.org/?Uniform+Resource+Locator http://www.w3.org/default.html#Introduction ftp://wuarchive.wustl.edu/mirrors/msdos/graphics/gifkit.zip ftp://spy:secret@ftp.acme.com/pub/topsecret/weapon.tgz mailto:fred@doc.ic.ac.uk news:alt.hypertext telnet://dra.com
The part before the first colon specifies the access scheme or
protocol. 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 same host. Other less commonly used schemes include
news,
telnet or mailto (
e-mail).
The part after the colon is interpreted according to the access scheme. In general, two slashes after the colon introduce a
hostname (host:port is also valid, or for
FTP user:passwd@host or user@host). The
port number is usually omitted 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 is usually related to the pathname of a file on the server. The file can contain any type of data but only certain types are interpreted directly by most
browsers. These include
HTML and images in
gif or
jpeg format. The file's type is given by a
MIME type in the HTTP headers returned by the server, e.g. "text/html", "image/gif", and is usually also indicated by its
filename extension. A file whose type is not recognised directly by the browser may be passed to an external "viewer"
application, e.g. a sound player.
The last (optional) part of the URL may be a query string preceded by "?" or a "fragment identifier" preceded by "#". The later indicates a particular position within the specified document.
Only alphanumerics, reserved characters (:/?#"%+) used for their reserved purposes and "$", "-", "_", ".", "&", "+" are safe and may be transmitted unencoded. Other characters are encoded as a "%" followed by two hexadecimal digits. Space may also be encoded as "+". Standard
SGML "&;" character entity encodings (e.g. "é") are also accepted when URLs are embedded in HTML. The terminating semicolon may be omitted if & is followed by a non-letter character.
The authoritative W3C URL specification.
(2000-02-17)
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