POV: date=October 2008 Expand: date=March 2008

In computing, a Uniform Resource Locator (URL) is a Uniform Resource Identifier (URI) which also specifies where the identified resource is available and the protocol for retrieving it. In popular usage and in many technical documents it is often confused as a synonym for uniform resource identifier.

Syntax

main: URI scheme#Generic syntax Every URL begins with the scheme name that defines its namespace, purpose, and the syntax of the remaining part of the URL. Most Web-enabled programs will try to dereference a URL according to the semantics of its scheme and a context-vbn. For example, a Web browser will usually dereference the URL http://example.org/ by performing an HTTP request to the host example.org, at the default HTTP port (port 80). Dereferencing the URL 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 website.

The hostname portion of a URL, if present, is case insensitive (since the 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:

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

URLs as locators

In its current strict technical meaning, a URL is a URI that, “in addition to identifying a resource, 1 a means of locating the resource by describing its primary access mechanism (e.g., its network ‘location').”Tim Berners-Lee, Roy T. Fielding, Larry Masinter. (January 2005). “Uniform Resource Identifier (URI): Generic Syntax”. Internet Society. RFC 3986; STD 66.

Internet hostnames

main: 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.