1. A Method for mapping an XML data structure to an ontology comprising: providing an XML document with a corresponding XML schema definition; a) mapping XML schema declarations and definitions to ontology schema definitions in the following way: mapping XML element and attribute declarations to ontology property definition; mapping XML complexType definitions to ontology class definitions; b) if information (PSVI annotation) from the validation of the XML document by the XML schema is used, mapping XML nodes with a known PSVI-type in the following way to ontology instances: mapping PSVI complexType annotations to ontology class instances; mapping element and attribute nodes to ontology property instances; c) defining the following predefined ontology schema definitions: defining a predefined ontology class definition and a predefined ontology datatype property definition and a predefined object property definition; d) if the XML document has been validated by the XML schema, mapping XML nodes without PSVI-type annotation to ontology instances and ontology definitions in the following way: mapping XML element and attribute nodes to ontology property instances and ontology class instances.