XLink

XML Linking Language, or XLink, is an XML markup language and W3C specification that provides methods for creating internal and external links within XML documents, and associating metadata with those links.

XLink 1.1 is a W3C recommendation and the successor of XLink 1.0, which was also a W3C recommendation.

XLink defines a set of attributes that may be added to elements of other XML namespaces. XLink provides two kinds of hyperlinking for use in XML documents. Simple links connect only two resources, similar to HTML links. Extended links can link an arbitrary number of resources.

A simple link creates a unidirectional hyperlink from one element to another via a URI. Example:

Extended links allow multiple resources, either remote or local, to be connected by multiple arcs. An arc is information about the origin, destination and behavior of a link between two resources. The origin and destination resources are defined by labels. By using one or more arcs, an extended link can achieve specific sets of connections between multiple resources.

For example, if all resources in an extended link were given the label A, then an arc within that link declaring from="A", to="A" would form connections between all resources.

Extended links do not need to be contained in the same document as the elements they link to. This makes it possible to associate metadata or other supplementary information with resources without editing those resources.

XLink also supports richer information about link types and the roles of each resource in an arc.

Hypertext links in Scalable Vector Graphics can currently be defined as simple XLinks. The working draft of SVG 1.2 proposes using extended XLinks as well. In the SVG 2 specification, XLink was deprecated in favor of non-namespaced equivalent attributes.

The Resource Directory Description Language, an extension to XHTML Basic that is used to describe XML Namespaces, uses simple XLinks.

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