absoluteURI

An absoluteURI (often written as absolute URI) is a Uniform Resource Identifier that contains a scheme and therefore identifies a resource independently of any base URI. In RFC 3986, an absolute URI has the form scheme: hier-part [ ? query ] [ # fragment ]. For example, https://www.example.com/path?query=1#frag is an absolute URI.

A relative URI lacks a scheme and must be resolved against a base URI to form an absolute URI. Examples include /images/logo.png (a path-relative reference) or ../docs/manual.pdf. Relative URIs are convenient for referencing resources within the same site or document collection and rely on a base for disambiguation.

In practice, absolute URIs are used to locate resources on the network and are commonly manipulated in software that parses or generates links. Web browsers, XML processors, and other tools resolve relative references by combining them with a base URI to produce an absolute URI for retrieval or processing. Distinctions between absolute URIs and other forms of identifiers are important for correctness, link validation, and resource resolution.

The terms URL, URI, and URN relate to this concept. Every URL is a URI, but not every URI is a URL. An absolute URI that also identifies a resource by its location, usually with a recognizable scheme such as http or https, is often referred to as a URL. Absolute URIs may include components such as authority, path, query, and fragment.

Unicode and IRIs extend the concept further. Internationalized Resource Identifiers allow Unicode, which can be represented in absolute URIs through percent-encoding when transmitted or stored, ensuring compatibility across systems. Many libraries provide methods to test for absoluteness (for example, isAbsolute) and to resolve relative references against a base.