The entire IFC EXPRESS schema (IFC entities and types and properties and so forth) is made available in one large ifcOWL ontology. In addition, the ifcOWL ontology uses some OWL classes and properties that are defined elsewhere. Namely, data types that are specific to EXPRESS (not to IFC) and to the representation of lists are defined in the following locations:

The ifcOWL ontology only imports the EXPRESS ontology. The EXPRESS ontology in turn imports the LIST ontology.


ifcOWL extensions
At the moment, one extension is available for the ifcOWL ontology. This extension represents the WR RULES defined in the original IFC schemas. The extension imports the ifcOWL ontology. It thus provides a more complete version of the ifcOWL ontology.