xlink

XLink, short for XML Linking Language, is a World Wide Web Consortium standard that defines a generic mechanism for creating hyperlinks within XML documents. It provides a way to express both simple links and more complex, multi-resource relationships that may span several documents or namespaces. The XLink model introduces a small vocabulary of constructs that can be used within any XML vocabulary to describe how resources are related and how links should be presented or retrieved.

Core concepts in XLink are link, locator, and arc. A link element groups one or more locators and arcs. A locator identifies a target resource, typically via a URL, while an arc defines a relationship between resources, connecting locators to express how they relate. By combining these components, extended linking can express relationships that go beyond a single destination. Elements can be typed with values such as simple, extended, locator, or arc, and optional attributes like show and actuate provide guidance on how a link should be presented to the user and when the linked resource should be loaded.

Namespace usage and attributes are a notable part of XLink. The specification uses the xlink namespace and supports attributes such as href, type, role, title, show, and actuate to qualify links and control behavior. In practice, XLink provides a flexible, standards-based approach to linking that can be embedded in various XML vocabularies, including markup languages and data formats.

Adoption and legacy status: XLink influenced linking practices in some XML standards, most notably certain versions of SVG, which used xlink:href for references. However, the approach proved complex for many use cases, and with the rise of simpler linking patterns and RDF-based solutions, XLink saw limited adoption in new projects. Today it is largely regarded as a historical or niche mechanism for XML linking.