This paper presents a method to remove the dependency of XML access
control models on the syntactic representation of the XML trees.  We
propose a semantics-based approach, expressing XML access control
on ontologies that describe the XML documents.  Then the semantics-based
security model is transformed to the syntactic representation on the actual
XML instances.  Our method supports the uniform enforcement of an
authentication model on syntactically different but semantically equivalent
XML documents.