Linking in XML is divided into multiple parts:
A Uniform Resource Identifier (URI) names or locates a resource
An XLink defines connections between two or more documents identified by URIs
XPath identifies particular nodes within a document
An XPointer adds an XPath to a URI
XML Base (a.k.a. XBase) defines the URI against which relative URIs are resolved
XInclude embeds a document identified by a URI inside an XML document.