uniform resource locator

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.

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 open a "Compose e-mail" window 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.

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’).”^[1]

Address bar

Address Bar in Microsoft Internet Explorer.

URLs are typically entered into the address or location bar of a web browser. To the right is a standard Microsoft Internet Explorer address bar. Address bars may of course vary in appearance depending on which web browser it is displayed in, and which skin is in use.

Clean URLs

"Clean" and "cruft-free" describe URLs which are:

• Not tied to technical details, such as the software used or whether the resource comes from a file or a database - so that a change in the technology will not break existing links to the resource. e.g. /cars/audi/ is preferable to /cars/audi/index.php or /myprog.jsp?page=cars/audi/.
• Not tied to internal organisational structure, such as the current editor or department that created the document - so an internal reorganisation will not cause existing links to the document to break. e.g. /recommendations/2007/xyz/ is better than /~users/jane/current-work/xyz/ or /xyz-team/recommendations/.
• Consistent with other URLs in the same site in terms of hierarchy. This is desirable so a user can see where they are in the structure of the site, and can predict where to find what they are looking for. e.g. /cars/audi/ and /cars/ford/, instead of /cars/audi/ but /ford-cars/.
• Consistent with other URLs in the same site in terms of action. This is desirable so a user can predict other, similar URLs on that site, e.g. if /blogs/andrea/feed/ shows a feed of Andrea's blog, then appending /feed/ to any another blog on the same site should show a feed for that blog.
• A single location for a single resource. The same resource should not be available from multiple URLs, as this results in both confusion (Are they the same resource, or is one a copy of the other? Which is the 'right' one? Is one new and the other due to be removed?) and technical difficulties, e.g. counting links to a particular resource, or caching content to speed up access but not being able to show the cached content when the resource is accessed using a different URL.

An example of the difference between "clean" and "standard" URLs could be seen as:

Standard: http://example.com/index.php?section=articles&subsection=recent

Clean: http://example.com/articles/recent/ or http://example.com/articles/2007/

See also

External links

• Cool URIs don't change
• RFC-3986 Uniform Resource Identifier (URI): Generic Syntax
• RFC 1738
• RFC-3986 (html)

References

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