While many of the W3C's efforts are still in the discussion phase, some initiatives, such as HTML 4.0’s successor, XHTML, have made it to final recommendations. And the W3C continues to push for standardization of information exchange on the Web with farsighted recommendations for the XML protocol. One such group of associated language definitions is XLink and XBase.
XML developers understand the advantage of tying together documents, and the XLink standard provides this capability. XLink defines a series of global attributes, which XML developers can use to identify linking elements that support creation of unidirectional (similar to HTML hyperlinks) or complex linking structures.
XLink defines a link as an explicit relationship between two resources or parts of resources. A resource is any addressable unit of information or service. XLink uses the standard uniform resource identifier (URI) reference to describe the link.
For example, you can create a link from an XML element to a file, image, program, or query result. To use XLink, the developer must include the standard XLink namespace definition.
Here's a look at XLink's attributes:
- type: This identifies the element as an XLink element. Options include simple, extended, locator, resource, arc, and title.
- href: This identifies the linked URI.
- role, arcrole, title: These describe semantic information for the link.
- show, actuate: These describe behavior attributes for the linked element.
- label, from, to: These describe traversal attributes for the linked element.
XLink requires support for HTML 4.0 linking constructs, and the XBase definition is the recommendation that accomplishes this goal. XBase allows the creation of the base URI that authors of XML documents can use to address URIs as relative references to the document's base URI.
To do this, developers apply a new document attribute that identifies the document's root structure. Developers can then create all other XLink references relative to this base.
For more information about XLink and XBase, check out the W3C's XLink and XBase Web pages.