## 2 Literature Review
For instance, CityGML [26] is an international standard data model published by the Open Geospatial Consortium (OGC) in 2008 (developed since 2002) to represent multiscale 3D information about entities of cities. It is an open data model for the storage and exchange of 3D city models. Concerning the architectural heritage, the IFC (Industry Foundation Classes) in the BIM (Building Information Model) environment for parametric modelling must be considered [27]. Regarding the documentation of CH, it is possible to mention two primary standards: the International Committee for Documentation (CIDOC)-CRM (CIDOC conceptual reference model) core ontology [28] and the Getty AAT (Art and Architecture Thesaurus). The CIDOC-CRM was developed by the International Committee for Documentation (CIDOC) of the International Council of Monuments (ICOM) and is the core ontology for managing cultural heritage information, now standard ISO 21127 [29]. This standard is aimed at enabling the exchange and integration of information between heterogeneous data sources. It was initially developed for the representation of the knowledge of museum objects. The Getty vocabularies [30] propose terms connected to cultural heritage, as premiere references to categorise works of art, architecture, material culture, the names of artists or architects, as well as the geographic categories. One of these is the Art and Architecture Thesaurus (AAT) to describe works of art and architecture. Terms in the AAT may be used to describe art, architecture, decorative arts, material culture, and archival materials. The target audience includes museums, libraries, visual resource collections, archives, conservation projects, cataloguing projects, and bibliographic projects. Recently, the Getty vocabularies also developed a SPARQL version of the thesaurus available on-line [31]. In brief, despite many studies, there is no existing ontology or standard that provides a complete semantic formalisation of HBH and their elements. Nevertheless, there is a wealth of knowledge in terms of core ontologies and legislation documents that could serve as a basis for developing a more adapted domain ontology for the exploration of historical buildings. In this framework, it is possible to mention various studies focused on combining 3D modelling of HBH, precisely HBIM, and knowledge-based or ontological approaches, reusing existing knowledge and standards in the domain of geographic information and built heritage representation. Such an ontology can, subsequently, be used to bridge semantic and geometrical/topological information acquired with advanced technologies (e.g., LiDAR point clouds) to generate parametric structured models of built heritage for their effective documentation, preservation, valorisation, and restoration. Proposed Ontology-Based Method for the Generation of Parametric Structured Models for Historical Built Heritage  
Here we propose a workflow for the conceptualisation and 3D modelling of selected domains of HBH in particular castles and fortified structures in historical centres. The proposed workflow is composed of several steps that allow bridging between an ontological representation of the historical sites with their effective 3D representation using a detailed LiDAR data set. The present study adapts the following reproducible workflow (illustrated in Figure 1):  
1. The selection of castles and fortified structures as archetypal models and definitions, and the identification of geometrical characterisation (morphology) of building elements starting from case studies (Section 3.1). 2. A survey and analysis of existing descriptions referred to as HBH in vocabularies and standards, to spatially represent them (Section 3.2). 3. Reasoning about morphology from case studies analyses (Section 3.3). 4. Ontology development (Section 4). Figure 1: Proposed methodological workflow and its levels.