# IFC Classification for FOSS HBIM: Open Issues and a Schema Proposal for Cultural Heritage Assets
## 2 IFC Customization and Proposal for Heritage Assets
### Schema Proposal for Heritage Assets
After the inclusion of ad hoc definitions, the components of the column can be correctly classified: the custom \"_ifcRole_\" _capital_, included inside the ARCH_COMPONENT module, can be assigned to the decorated capital of the column; _shaft_\"_ifcRole_\", considered as the role of _ifcColumn_ (inside the ARCH_STRUCTURE module), can be assigned to the central vertical part of the column (shaft); _base_\"_ifcRole_\", included inside the ARCH_COMPONENT module, can be assigned to the lower support of the column (base). By modifying and implementing the ARCH_ROOF module, other particular typologies of ceilings and roofs can be included, following the attributes and properties of main entities. A medieval vaulted system (consisting of a rib vault) has been used as an example for semantic IFC classification inside the custom HBIM platform (Figures 5 and 6). Figure 4: Example of ionic column. **(A)** Ionic column subdivisions: capital in blue; column shaft in red; base in green. **(B)** FreeCAD experimentation: IFC classification of the ionic capital by using custom roles available on the drop-down menu after the implementation. Figure 5: Example of a medieval rib vault: IFC classification of ribs by using custom roles available on the drop-down menu after the implementation. Moreover, documenting and analyzing a medieval rib vault it can be considered both as _roof_ element and _structural_ element due to its ribs supporting vaults; then, following this line of thought, the custom roles of _rib_ and _vault_ have been included inside the ARCH_ROOF and ARCH_STRUCTURE modules of the ARCH workbench. In this way, a rib vault can be semantically and structurally classified following its components and their behaviors. The third example has been a medieval wall consisting of stone masonry, a single-lancet window contemporary with the main construction site and its plaster/render layer can be documented and classified by using custom definitions implemented in default Python files of FreeCAD (Figures 7-11). Looking at the building stratigraphy, the single-lancet window, being in the same construction temporal phase with the principal stone masonry, could be inscribed into the principal stone masonry and then become part of the masonry (ifcWall). However, it must be classified as an architectural element (EA) and then it has to be assigned to an IFC custom family: in this case, the already implemented definition _single-lancet window_ has been used as a role of ARCH_WINDOW in FreeCAD 0.17 and as a custom role of the STRUCTURE entity inside the generic BIM objects list of FreeCAD 0.18. The principal masonry unit as well as render/plaster unit could be classified by using the already implemented USM and USR definitions, designed as roles of the ifcWall entity, being fundamental components of the medieval wall. The here presented conceptual medieval stone wall, which includes also a single-lancet window and a plaster/render layer, is undoubtedly a particular example. It allows different interpretations that can be extracted from the stratigraphic analysis, depending especially on surveyor interpretation (subjective analysis). This analysis may not be the only one that can be extracted from stratigraphy. Archaeological analyses, like most humanities studies, are essentially based on different kinds of data, in addition to the information extractable from the surveyed context: from paper-based analyses to 2D drawings, from archive research to alphanumerical diagrams. These collected data are essentially used in order to make historical interpretations or to reconstruct an historical event (based on archaeological evidence). By definition, interpretation has a strong subjective factor and the hypothetic IFC classification is directly proportional to subjective analyses carried out by archaeologists or historians. For this reason, IFC definitions for historic architecture elements and stratigraphic units detectable on masonries could assume different keys of reading.