General

Sources

IfcOwl is the generic name for RDF/OWL equivalents of IFC, which is originally formulated in EXPRESS. IfcOwl was initially proposed in 2016 by Pieter Pauwels and Walter Terkaj.

IfcOwl is documented here on the buildingSMART website.

Provisional version used here, matching IFC 4.3 ADD2, is available on this website.

Alternatives

Other ontologies for BIM

(about BOT)

Other technologies: Labeled Property Graph

In 2023, Zhu Junxiang et al. proposed an alternative representation of IFC classes using a Labeled Property Graph implemented in Neo4J Zhu01(#Zhu01).

Evolution

The announced evolution towards IFC 5 is documented in the public IFC 5 Github. IFC 5 is currently at alpha stage.

For serialization, the goal of IFC 5 is to evolve towards JSON while ensuring a transition from the current STEP format. For the modeling part, UML was evoked as a possible replacement for EXPRESS. The IFC 5 Github does not currently expose works in that field. On the other hand, sample serialized data in the Github identify their type by referring to a bSDD URL. bSDD itself can be seen as a a sort of ontology with ample metadata (definitions, references), while Descriptive Logic aspects such as class hierarchies are textually described but not directly computable.

Note: IFC makes extensive use of EXPRESS functions and rules. Such functions and rules were outside scope of IfcOwl in 2017 bSI01, sections 2.8 and 2.9(#bSI01) and are not to be found in later versions. Functions and rules cannot generally be expressed in UML class diagrams and would logically require OCL (Object Constraint Language, specified under UML 1.1 ff. since 1997). Whether and when they could be implemented as SHACL shapes, complementing a future version of IfcOWL, is an open debate. See also Issue #44 on the IFC 5 Github.

In the future, the most likely scenario(s) would be (awaiting confirmation by bSI):

• bSI maintaining IfcOwl in parallel to other formal representations (UML) and Web publication (bSDD), requiring a limited update of the model transformation principles (UML to OWL) and tools.

Encountered issues

IfcOwl "per se"

Loading IfcOwl 4.3 ADD2 in Protégé reveals 27 unsatisfiable classes (reasoner: Pellet or HermiT). Importing IfcOwl in RSM in another tool (Eddy 3.7, using HermiT) leads to the same result.

Interfacing IfcOwl with other CDM components

References

[bSI01]: buildingSMART final standard: The IfcOWL ontology. Published by buildingSMART International on March 29, 2017.

[Zhu01]: IFC-graph for facilitating building information access and query, Zhu Junxiang & al., in Automation in Construction 148 (2023) 104778