## 2 Literature Review  
In order to conceptualise and represent building components, several well-known standards have been developed during the past decades. This includes 3D city models (considering standards such as CityGML by the Open Geospatial Consortium) and Building Information Models (BIM), for which the reference standards are the Industry Foundation Classes (IFC) developed by buildingSMART. The standards consider a higher level of representation, especially concerning interior parts of buildings, structures, component materials, etc. However, starting from the introduction of the use of BIM technology for Heritage (HBIM) [8], it has become evident that one of the most problematic aspects of its application is the criticality of making the parametric approach compatible with the uniqueness of historical architecture. This is due to the geometric complexity of the artefacts, degradation and material characterisations: they are different from contemporary buildings, which count on a high level of industrialisation and, consequently, on higher repeatability of components and more simple shapes. Reverse engineering is usually necessary to suitably model historical buildings' components. This strategy and many consequent developments have been adopted to facilitate and better manage the maintenance of existing buildings [9; 10], for conservative and restoration requirements [11; 12] and also for the structural analysis and evaluation of historical architecture [13; 14; 15]. Precisely for these reasons, several efforts are directed to the database design with a particular focus on non-geometric information correlated to HBIM that is repeatable on different examples of heritage [16], with the harmonisation of vocabularies and repositories [17]. In the framework mentioned above, it is possible to collocate some already-made studies concerning standard classification in the built historical heritage domain; HBIM is linked to semantic-web studies and the ontology definition for historical centres and buildings. A starting point towards the creation of an ontology for small historical centres individuating useful classifications, descriptions, and concepts able to formalise the selected domain has been presented in [18]. Moreover, the development of identifying a path for historical fortified buildings and structures' semantic definitions underlining the multitude of use cases concerning HBH and historical urban architecture is proposed 7. [PERSON] et al. [19] reported the worldwide diffusion of integrated approaches that combine BIM (or HBIM) techniques with information management of semantic knowledge. [PERSON] et al., (2018) [20] showed a significant strategy for our present work: they combined HBIM models and the Getty Art and Architecture thesaurus (AAT) (a vocabulary for architectural elements' definitions, explained below) in SPARQL (an RDF query language), adding ID semantic information in the HBIM model parameters. This work presented a semantically enriched HBIM library for the elements of a castle. Other studies [21; 22] focused on the semantic enrichment of HBIM models (designed from a 3D metric survey) for the interpretation, management and querying of historical buildings organising knowledge using ontologies and databases to store hierarchical information and properties. As ref. [23] attempted to define IFC in an ontology language (OWL), they connected IFC and RDF, creating a new structure which resulted in an ifcOWL ontology. Very recently, some authors [24] worked to define an ontology-based database providing a vocabulary to query an HBIM model of vaults, and ref. [25] studied an integration workflow connecting HBIM modelling and ontological knowledge. Other research works attempt to use different standards and vocabularies from the geographic information domain for historical heritage representation.