The Conceptual Data Model (CDM) is a federation of models. Since the Shift2Rail LinX4Rail project (see public deliverable D8.3, 2023), IFC is an integral part of the Conceptual Data Model within the FP1-MOTIONAL project (see CDM-MOTIONAL for more details). IFC is and remains the property of buildingSmart International, and is under the full control of bSI.
IFC is natively expressed in EXPRESS, a rich but not-so-widespread formal language; see ISO10303 and the EXPRESS specification by OMG. IFC has an equivalent representation in RDF/OWL: see these technical explanations.
IFC releases (in various formats) are available on this bSI page. The IfcOWL version is not downloadable directly; see the Wiki for links.
The present repository hosts some general explanations about the usage of IFC in the context of the CDM: see the Wiki. Also, adapter vocabularies are proposed: these are small ontologies allowing smooth linkage of some particularly relevant IFC classes and properties with the rest of the CDM).