version: $Revision: 1.1 $ date: $Date: 2005/06/20 17:14:32 $ author: Jos de Bruijn, Reto Krummenacher this document provides an XML Schema for the XML version of the WRL syntax The syntax presented in this document can be used for all WRL variants. The WRL variant is identified through the 'variant' attribute of the root element 'wrl'. A modular approach has been chosen when creating this schema. This schema contains the conceptual syntax. Separate schemas have been developed for the WRL identifiers and for the WRL logical expressions. These schemas are therefore included in this schema. The element 'wrl' is the preferred root element for any WRL specification. It allows the user to explicity specify, through the 'variant' attribute, which WRL variant is used. If the WRL variant has not been specified, the application has to "guess" the variant and in the worst case, WRL-Full will be assumed. This element is used for indicating which ontologies to import. Importing ontologies is the most basic (and inflexible) modularization mechanism. The result of the import is merely the union of the axioms in the importing and the imported ontology. Any element can be used inside the non-functional properties. Non-functional properties function as annotation for the containing element. The recommended set of non-functional properties is the set of elements offered by Dublin Core. WRL further defines one element, named 'version'. An ontology specification. An axiom reference or specification. In case no elements are nested inside the axiom, it is merely a reference to an axiom definition. Otherwise, it is an axiom specification, consisting of a number of annotations in the form of non-functional properties and the actual logical expression, contained in the definedBy keyword. A concept specification or reference. In case no elements are nested inside the concept, it is a reference to the concept identified by the name. Otherwise, it is a concept specification. A concept can have zero or more attributes. The type of the attribute can be inferring or constraining. A constraining attribute (corresponding to 'ofType') is used to check the type of parameter values; an inferring parameter (corresponding to 'impliesType') is used to derive the type of attribute values. By default an attribute is constraining. Furthermore, an attribute can be symmetric, transitive, reflexive or the inverse of another attribute. Finally, it is possible to specify the minimal and maximal cardinality of an attribute. By default the minimal cardinality is 0 and the maximal cardinality is n (i.e. not restricted). A relation specification or reference. In case no elements are nested inside the relation, it is a reference to the relation identified by the name. Otherwise, it is a relation specification. The ordered list of parameter types An instance can be member of zero or more concepts. Furthermore, zero or more attribute values can be associated with this particular instance. The value of an attribute is either the identifier of another WRL element or a literal. An instance of a relation corresponds with a tuple in the extension of the relation. The values of the parameters are explicitly specified. In case the relation does not have named parameters, the parameter values only have a value and not a name. The order of the XML elements then corresponds with the order of the arguments of the relation.