# 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
Firstly, by following the 0.17 version of FreeCAD, this custom list has been sub-divided among different Python files mostly concerning ARCH_WALL, ARCH_STRUCTURE, ARCH_ROOF, ARCH_WINDOW and ARCH_COMPONENT principal macro entities. (Table 1). In FreeCAD version 0.18 (which has been used for practical demonstrations), the IFC implementation has been directly performed by editing the single _ArchComponent.py_ Python file (implementing previous custom types) because it contains _IFC types_ list, the _Property types_ list and the _Possible roles for FreeCAD BIM objects_, differently from previous versions of FreeCAD. Despite the original aim of IFC classification (for the AEC industry), Python files allow us to customize the \"_ifcRole_\" referring to FreeCAD macro elements and it has been performed regarding peculiarities of archaeological sites and building archaeology. The most important information derived from these disciplines is referred to as stratigraphy and its analysis is based on physical sequences among layers and units. Indeed, the stratigraphic method, derived from geological analyses and then from field archaeology, can be therefore applied in historical buildings (mostly medieval), and stratigraphic units (portions that compose the stratigraphy) can be analyzed and documented through the edges. Stratographic units (US) can be mostly referred to as positive (accumulation of materials) and negative (removing activities) actions and can be also referred to in terms of different compositions: for example, in building archaeology, field principal differences are related to masonry units (USM), render/plaster units (USR) as well as architectural elements (EA). FreeCAD classification concerning the archaeological documentation method may include the classification of archaeological units as archaeological evidence, including all reference unit typologies [25]: masonry stratigraphic unit (USM), render/plaster stratigraphic unit (USR), architectural element (EA), architectural complex (CA), block of the building (CF), general elevation (PG), particular elevation (PP), horizontal structure (SO), functional unit (UF). These classifications might be included in FreeCAD 0.17 inside macro entities like ARCH_WALL, ARCH_STRUCTURE and ARCH_COMPONENT, from the biggest to the smallest unit. In the FreeCAD platform, the classification referring to masonry and render/plaster units detectable in building archaeology contexts has been included. USM and USR classification has been designed as custom \"_ifcRole_\" of _ifcWall_ entity, since these unit typologies are part of walls and masonries. This classification could also be developed by exploiting _ifcMaterialLayerSets_ inside the IFC2x3 schema and by defining materials' layers and thicknesses (analyzing units in more detail). However, in this project, the main focus has been an early attribution of typological (and more generic) definitions to particular heritage assets via FreeCAD possibilities. After the implementation inside the Python file of the FreeCAD folder root, modifications become available on the FreeCAD interface inside the drop-down menu referring to \"_ifcRole_\": attributes and properties of new classification refer to general and structural behaviors of the principal entities which they rely on. After this implementation, different experimentations have been carried out by using some examples concerning heritage assets: an ionic column, a rib vault and a medieval masonry. These patterns have been examined and documented in order to validate the proposed IFC classification. An ionic column (Figure 4), consisting of a base, a shaft and a capital, can be therefore documented and semantically analyzed by using the FreeCAD custom HBIM platform.