OWL representation of the buildingSMART data model. The IFC data model is written in an EXPRESS schema (IFC2x3). This ontology is the result of an automated transformation of this EXPRESS schema into an OWL ontology. In this transformation process, every EXPRESS element that has a direct equivalent in OWL is mapped onto this equivalent. More specifically, for each ENTITY element in EXPRESS a corresponding OWL class is generated, EXPRESS attributes are converted into the appropriate OWL properties, etc.