# An Inspection of IFC Models from Practice
## 4 Methodology
### Models Inspection
#### 4.3.1 Inspection and Assessment of Semantics  
A correct use of semantics within the models is essential to select and retrieve the correct objects within models, as well as to possibly exclude some of them from calculations.  
The most basic requirement is that the objects are stored by means of the correct IFC entity, which allows their consistent identification, although possible differences are due to slightly different interpretations of the IFC classes or various generalization levels (i.e., super-classes used instead of sub-classes).  
For this reason, the consistency of used entities with respect to the IFC data model definitions was checked, giving scores to the models as:  
**1**: all correctly used;  
**0.8**: correctly used, with few errors;  
**0.5**: partially consistent;  
**0.3**: few consistent entities;  
**0**: completely wrong.  
A second check with respect to the same aspect was about the use of _IfcBuildingElementProxy_, that is useful to include in the representation elements not foreseen by the IFC model, but can be wrongly used to substitute entities having a valid representation in IFC.  
In this case, the scores were given as:  
**1** none used;  
**0.9** present but used correctly (that is, to represent entities not present in IFC);  
**0.5** some (i.e., only a couple of elements or kinds of elements) are used, instead of correct classes;  
**0.3** many different ones are used, instead of the correct classes;  
**0** all entities are _IfcBuildingElementProxies_.  
The rich semantics allowed by BIM and IFC do not end with the use of entities, but a number of properties and attributes can additionally be an effective support for many use cases. In particular, materials and their own properties are essential to a number of applications (such as energy simulations, cost computations, noise simulation and so on). For this reason, a specific check was dedicated to this aspect.  
However, it was hard to give scores because on the one hand, they could correctly include a varying number of attributes and properties, foreseen by the IFC schema or added as extensions. On the other hand, the information for each use case was very specific and it would be necessary to consider this in detail in order to give an appropriate overview about the completeness and suitability of the stored information.  
Therefore, attributes were assessed as:  
**1**: using many attributes fully true to the definition of the IFC schema (which appeared to be never the case);  
**0.9**: using many attributes both foreseen by IFC and added custom ones;  
**0.8**: using few attributes both foreseen by IFC and added custom ones;  
**0**: not used at all.  
For the reasons previously mentioned, in this part of the study, all the assigned scores were considered higher than the minimum requirements, except the case where there were no attributes at all.  
Similarly, materials were just noted as present (1) or not present (0), plus a score \"0.5\" in the cases when they were present, but in a very inaccurate way, by means of few very general indications (such as just \"wood\").