# An Inspection of IFC Models from Practice
## 1 Introduction  
Interoperability is a key feature for data to be exchanged and (re)used in new-generation applications for the planning, building, analysis and management of cities, as well as for collaboration and communication. Among such data, an important source of information about the built environment are Building Information Models (BIMs). They were developed in the Architecture Engineering and Construction (AEC) field approximately from the 1980s, as an evolution of Computer Aided Design (CAD) tools, and have become more popular during the last 20 years, with the development of cheaper and more powerful computers, and more effective tools to model and manage BIMs. The original scope of such (often 3D) information systems is to support a building's design and construction. However, current BIM models are supposed to be useful for much more than this narrow purpose, representing a central platform for collaboration during the design phase of a building (architectural design, structural design, installations design, etc. ), supporting coordination between disciplines and analysis of the designed building within the same modelling tool or within compatible ones, and once built, being a base data set that can be reused and maintained to support the asset and facility management of the modelled object. Great advantages would be brought by an effective interoperability of such data. These would involve many scopes. First of all, the collaboration among different kinds of practitioners involved in building design, construction and management. Second, the exchange and reuse of the data among different stakeholders and through time. Third, the integration with other data sets, including different formats, for various use cases (e.g., map updates, energy analysis, building permits issuing, materials documentation and soon). For instance, an often discussed integration is the one with 3D city models and other types of geoinformation (GeoBIM), cf. [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. One solution to realize these potentials could be the use of the same native format produced by (mostly proprietary) BIM software. However, from the point of view of developers and users, a more preferable and realistic solution would be the use of open standard formats; in particular, for BIM, the Industry Foundation Classes (IFC) ([[https://technical.buildingsmart.org/standards/ifc/](https://technical.buildingsmart.org/standards/ifc/)]([https://technical.buildingsmart.org/standards/ifc/](https://technical.buildingsmart.org/standards/ifc/)), accessed on 1 March 2021) which were developed by the buildingSMART consortium ([[https://www.buildingsmart.org](https://www.buildingsmart.org)]([https://www.buildingsmart.org](https://www.buildingsmart.org)), accessed on 1 March 2021) (Section 2). This approach ensures an equal footing for different software vendors and avoids vendor lock-in for users. The use of open standard formats is also preferable in the case of integration with data sets from different fields or in different formats, where potential users might not have any software that is capable of reading a given proprietary format. However, some issues can still be encountered when producing [18; 19] and exchanging standardized data among software and people (such as incompleteness of the models, inaccuracies, different semantics interpretations, geometry deformations) [20; 21; 22; 23; 24], which could prevent a smooth exchange of information as well as the use of data within automatic processing [25; 26]. It is fundamental to overcome such problems and uncertainties to build interoperability on a solid base, for which the first step is the understanding of the state of the art. To connect to what is the current practice in the modelling and exporting of standardized BIM data by practitioners, a sample of BIMs, modelled within practitioners' design projects and provided in the IFC format, was inspected and analyzed (Section 4).