Uniform Resource Locator

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Related to Uniform Resourse Locator: universal resource locator, Uniform Resource Identifier

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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Uniform Resource Locator

(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://w3.org/default.html http://acme.co.uk:8080/images/map.gif http://foldoc.org/?Uniform+Resource+Locator http://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 "&<name>;" character entity encodings (e.g. "é") are also accepted when URLs are embedded in HTML. The terminating semicolon may be omitted if &<name> is followed by a non-letter character.

The authoritative W3C URL specification.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)


(Uniform Resource Locator) The address that defines the route to a file on an Internet server (Web server, mail server, etc.). URLs are typed into a Web browser to access Web pages and files, and URLs are embedded within the pages themselves as links (see hypertext).

The URL contains the protocol prefix, port number, domain name, subdirectory names and file name. If a port number is not stated in the address, port 80 is used as the default for Web traffic (HTTP traffic). See port 80 and TCP/IP port.

Downloading the Home Page
To access a home page on a website, only the protocol and domain name are required. For example, http://www.computerlanguage.com retrieves the home page of the Computer Language Company's website. HTTP is the Web protocol, and WWW.COMPUTERLANGUAGE.COM is the domain name. Browsers default to the http:// prefix so only the www.computerlanguage.com needs to be typed in. In fact, you can usually omit the WWW and dot, because most websites treat blank hostnames as "www" hostnames. Sometimes, you can even omit the .com, and the browser fills it in automatically.

Another Web Page
If a page is not the home page, its name has to be part of the address, and a slash is used to separate it from the domain name. For example http://www.computerlanguage.com/about.htm points to the About page (about.htm file). See URL shortening.

The Full Path
If a page is stored in a subdirectory (folder within a folder), its name is also separated by a slash, and subdirectories can be several levels deep. Follow the example below:
Hypothetical URL:


 This:          Is the:

 http://        protocol

 www.car.com/   domain

 kia/           subdirectory

 used/          subdirectory

 2008.html      file (Web page)

Is It a URL or a URI?

Technically, a URL is a type of uniform resource identifier (URI). Since most URIs are URLs, "URL" is the term more commonly heard. See URI.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
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