XLink Elements and Attributes
XLink offers two kinds of links:
Extended links
Extended links offer full XLink functionality, such as inbound and third-party arcs, as well as links that have arbitrary numbers of participating resources. As a result, their structure can be fairly complex, including elements for pointing to remote resources, elements for containing local resources, elements for specifying arc traversal rules, and elements for specifying human-readable resource and arc titles.
XLink defines a way to give an extended link special semantics for finding linkbases; used in this fashion, an extended link helps an XLink application process other links.
Simple links
Simple links offer shorthand syntax for a common kind of link, an outbound link with exactly two participating resources (into which category HTML-style A and IMG links fall). Because simple links offer less functionality than extended links, they have no special internal structure.
While simple links are conceptually a subset of extended links, they are syntactically different. For example, to convert a simple link into an extended link, several structural changes would be needed.
The following sections define the XLink elements and attributes.
Read more:http://www.w3.org/TR/xlink/