Linking in XML is divided into three parts, XLinks, XPointer, and XPath.
XLinks
XPointers
XPath
XLink, the XML Linking Language, defines how one document links to another document. XPointer, the XML Pointer Language, defines how individual parts of a document are addressed. XPath is a syntax used in XPointers for identifying particular nodes in an XML document's tree.
An XLink points to a URI (in practice, a URL) that specifies a particular resource. This URL may include an XPointer part that more specifically identifies the desired part or section of the targeted resource or document. XPointers use the XPath syntax shared with XSL to identify particular elements in the document tree.