Linking in XML is divided into multiple parts:
A Uniform Resource Identifier (URI) identifies a resource by name or location:
Uniform Resource Locators (URLs) locate resources
Uniform Resource Names (URNs) name resources
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
XBase defines the URI against which relative URIs are resolved
XInclude embeds a document identified by a URI inside an XML document.