XLink

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XLink

The XML Linking Language, or XLink, is an XML markup language used for creating hyperlinks for XML documents. XLink is a W3C specification which describes methods for allowing elements to be inserted into XML documents in order to create and describe links between resources, whether internal or external to the original document.

The XLink specification

XLink 1.0 remains the current version of XLink where it received W3C Recommendation status on 2001-06-27. The W3C brought XLink 1.1 to W3C Candidate status on 2006-03-28.

Linking with XLink

Xlink defines a set of attributes, which may be added to elements of another XML namespace. Xlink provides two kinds of hyperlinking for use in XML documents. Extended links are out-of-band hyperlinks that, in a linkbase document, can link resources over which the link editor has no control. Simple links offer similar functionality to HTML links, which are in-band links.

Simple links

A simple link is similar to links familiar from HTML; it simply creates a unidirectional hyperlink arc from one element of a web document to another via a URI. Example:



 Some Document
 The Some Document header.

Extended links

The XLink specification supports not only simple links but also extended links. Extended links allow multiple resources, either remote or local, to be connected by multiple arcs. Arcs are explicitly unidirectional - they only define traversal in a single direction. By grouping resources with labels and using one or more arcs, an extended link can achieve specific traversal pathways among the resources.

For example, if all resources in an extended link were given the label A, then an arc within that link which was from="A", to="A" would connect every resource to every other resourcce, and allow traversal from any of those resources to any other of those resources.

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

XLink also supports richer information about link types and the roles for each resource that an XLink connects.

Uses of XLink

Software support for XLink as of 2006-06 includes the following:

Mozilla Firefox

Mozilla Firefox (1.5.0) has some very limited support for simple XLinks.

Links with xlink:show="embed" do not work.
Links with xlink:actuate="onLoad" work if they are the only thing on the page.
All other links open the target in the current window, when requested, irrespective of the xlink:actuate or xlink:show attributes.

Netscape

Netscape (7.2) has the same support for simple XLinks as Firefox, except that the xlink:show="new" works correctly.

SVG applications

Hypertext links in SVG can currently be defined as XLink simple links. The Working Draft of SVG 1.2 proposes using XLink extended links as well.

RDDL

The XML language RDDL, an extension to XHTML Basic that is used to describe XML Namespaces, uses XLink simple links.

XBRL

The XML Language XBRL, eXtensible Business Reporting Language, has used XLink simple and extended links since the XBRL 2.0 specification was published in 2001. Most large XBRL taxonomies contain extensive linkbases. As of 2006, XBRL is probably the most extensive use of XLink in production systems.

References

External links

Markup languages | XML-based standards | W3C standards

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