Uniform Resource Locator

From Wikipedia, the free encyclopedia

This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007)

Please help improve this article or section by expanding it.
Further information might be found on the talk page or at requests for expansion. (March 2008)

"URL" redirects here. For other uses, see URL (disambiguation).

Uniform Resource Locator (URL), is a technical, Web-related term used in two distinct meanings:

In popular usage and many technical documents, it is a synonym for Uniform Resource Identifier (URI). In popular usage, it means a web page address.
Strictly, it is a compact string of characters for a resource available via the Internet^[1]. 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.

1 URI/URL syntax in brief
2 URLs as locators
3 Internet hostnames
4 Address bar
5 See also
6 References
7 External links

[edit] URI/URL syntax in brief

Main article: URI scheme#Generic syntax

Every URI (and therefore, every URL) begins with the scheme name that defines its namespace, purpose, and the syntax of the remaining part of the URI. Most Web-enabled programs will try to dereference a URI according to the semantics of its scheme and a context-vbn. For example, a Web browser will usually dereference a http://example.org/ by performing an HTTP request to the host example.org, at the default HTTP port (see Port 80). Dereferencing the URI mailto:bob@example.com will usually start an e-mail composer with the address bob@example.com in the To field.

example.com is a domain name; an IP address or other network address might be used instead. In addition, URLs that specify https as a scheme (such as https://example.com/) normally denote a secure web site.

The hostname portion of a URL, if present, is case insensitive (since DNS is specified to ignore case); other parts are not required to be, but may be treated as case insensitive by some clients and servers, especially those that are based on Microsoft Windows. For example:

the links http://en.wikipedia.org/ and HTTP://EN.WIKIPEDIA.ORG/ both will open same page.
the link http://en.wikipedia.org/wiki/Url is correct, but link HTTP://EN.WIKIPEDIA.ORG/WIKI/URL/ will result in an HTTP 404 error page.

[edit] URLs as locators

In its current strict technical meaning, a URL is a URI that, “in addition to identifying a resource, [provides] a means of locating the resource by describing its primary access mechanism (e.g., its network ‘location’).”^[2]

[edit] Internet hostnames

Main article: Hostname

On the Internet, a hostname is a domain name assigned to a host computer. This is usually a combination of the host's local name with its parent domain's name. For example, "en.wikipedia.org" consists of a local hostname ("en") and the domain name "wikipedia.org". This kind of hostname is translated into an IP address via the local hosts file, or the Domain Name System (DNS) resolver. It is possible for a single host computer to have several hostnames; but generally the operating system of the host prefers to have one hostname that the host uses for itself.

Any domain name can also be a hostname, as long as the restrictions mentioned below are followed. So, for example, both "en.wikimedia.org" and "wikimedia.org" are hostnames because they both have IP addresses assigned to them. The domain name "pmtpa.wikimedia.org" is not a hostname since it does not have an IP address, but "rr.pmtpa.wikimedia.org" is a hostname. All hostnames are domain names, but not all domain names are hostnames.

[edit] Address bar

Main article: URL bar

Location bar in Mozilla Firefox.

URLs are typically entered into the address or location bar of a web browser. To the right is a standard Mozilla Firefox address entry. Address bars vary in appearance depending on the web browser displayed in.