# An Inspection of IFC Models from Practice
## 3 The Importance of IFC Models Quality for IFC Data Downstream Automation Use Cases  
An insight into the use cases that rely on IFC models further explains the relevance of outlining the current state of the models. More focused quality requirements can then be recommended consequently. The use cases for which the BIMs and the IFC data model were conceived can be many, as it is even possible to read in the buildingSMART website ([[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): \"IFC can define physical components of buildings, manufactured products, mechanical/electrical systems, as well as more abstract structural analysis models, energy analysis models, cost breakdowns, work schedules, and much, much more\". Building design, which is the priority use case, requires elements to be modelled correctly and clear geometries to be generated. This use case foresees the cooperation of several professionals around the same building. Therefore, it is necessary that each of them models elements accurately, such that clashes between different models reflect design problems that need to be fixed, and if no clashes occur, they should not occur in the real world either. On the other hand, one of the most frequent current uses of IFC models is visualization, for which few quality requirements are necessary, as long as the elements of interest can be viewed correctly. An approximate georeferencing to the correct location and orientation can improve visualization, but a few meters of tolerance usually make little difference, depending on the context. However, the overarching aim of building information modelling, as well as any other information system, is the automation of tasks and analysis. Therefore, additional applications (other than visualization) must be taken into account. The automatic calculation of building costs [35; 36] requires an accurate definition of semantics, including the correct storage of elements within IFC classes and the association of correct attributes related to the specific element properties, materials, and possible references to fabrication details. In addition, such elements must be modelled correctly, avoiding clashes and intersections, since this could lead to inaccuracies, whose importance vary together with the dimension and complexity of the building. Georeferencing is usually not very important in this case, with only minor dependent factors, such as the transport of building materials. For the structural analysis use case [37; 38], it is important to model the building elements with their correct semantics and correct geometry, and to associate the correct attributes about material structural properties and their design as load-bearing elements or not. The relevant grouping of elements, in this case, is about the identification of each structural-independent building or part of it. It can be effectively represented by means of _IfcBuilding_. Georeferencing is not relevant in this case either. Energy simulations [39; 40] need an accurate modelling of the building envelope, information about building form, materials' physical properties, the internal layout and the space boundary connectivity to support the building energy performance calculations, implying good semantics to correctly identify building elements (entities) and to describe their properties. [PERSON] et al. [34] shows that many of the assessed models did have errorsin their definitions of space boundaries. [PERSON] and [PERSON] [41] shows that many of the assessed models did have errors in their labelling of external elements (the 'IsExternal' property). In addition, the correct identification of building units and their function are important, as well as the modelling of spaces and thermal zoning in particular (possibly as _IfcZones_ in version 4 of IFC). The accuracy of geometry is important as well ([PERSON] et al.