XLink

"XLL" redirects here. For other uses, seeXLL (disambiguation).

For other uses, seeXlink (disambiguation).

XML Linking Language,orXLink,is anXMLmarkup languageandW3Cspecification that provides methods for creating internal and external links within XML documents, and associating metadata with those links.

The XLink specification

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

Linking with XLink

XLink defines a set ofattributesthat may be added to elements of otherXML namespaces.XLink provides two kinds of hyperlinking for use in XML documents.Simple linksconnect only two resources, similar toHTMLlinks.Extended linkscan link an arbitrary number of resources.

Simple links

Asimple linkcreates a unidirectionalhyperlinkfrom one element to another via aURI.Example:

<?xml version= "1.0"?>
<documentxmlns="http://example.org/xmlns/2002/document"xmlns:xlink="http:// w3.org/1999/xlink">
<headingid="someHeading">SomeDocument</heading>
<para>Hereis<anchorxlink:type="simple"xlink:href="#someHeading">alink</anchor>totheheader.</para>
<para>Itisananchorthatpointstotheelementwiththeid"someHeading"onthecurrentpage.</para>
</document>

Extended links

Extended linksallow multiple resources, either remote or local, to be connected by multiple arcs. Anarcis 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 labelA,then an arc within that link declaringfrom= "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.

Support for XLink

Within other specifications

SVG

Hypertext links inScalable Vector Graphicscan currently be defined as simple XLinks.Theworking draftof SVG 1.2 proposes using extended XLinks as well.In the SVG 2 specification, XLink was deprecated in favor of non-namespaced equivalent attributes.

RDDL

TheResource Directory Description Language,an extension toXHTML Basicthat is used to describeXML Namespaces,uses simple XLinks.

XBRL

TheeXtensible Business Reporting Languagehas used simple and extended XLinks since the XBRL 2.0 specification was published in 2001.Most large XBRL taxonomies contain extensive linkbases. As of 2009, XBRL is probably the most extensive use of XLink in production systems.

METS

TheMetadata Encoding and Transmission Standard,supported and maintained by theLibrary of Congressfor describing file aggregations, uses simple XLinks in pointing to file locations as well as linkbases which describe relationships among external files (though these restricttoandfromattributes to type IDREF instead of NMTOKEN).

GML

Geography Markup Languageuses simple XLinks to implement referencing. In particular, GML uses xlink:href to support a graph model for geospatial information. GML's graph model is essentially the same asRDF,on which early versions of GML were based. The GML specification constrains the semantics of XLinks to be essentially the same as rdf:resource (from the RDF/XML syntax) i.e. the referent can logically be placed in-line and the data is still valid.

Implementations

Mozilla Firefox

Mozilla Firefoxhas supported simple XLinks since version 1.5, but only forSVGandMathMLdocuments. It is unsupported in other XML documents.Only thexlink:href,xlink:show,xlink:targetandxlink:titleattributes are supported.

Prince

Princesupports simple XLinks.

External links

• W3C Recommendation
• W3C Recommendation (version 1.0)
• XLink: Who Cares?
• XML Linking Implementations (Last Updated 2000)
• Demo of XLinksforMozillabrowsers