# From Field Archaeology to Virtual Reconstruction: A Five Steps Method Using the Extended Matrix
## 1 Introduction  
In the past, virtual reconstructions have been the subject of debates among archaeologists [1, 2, 3, 4, 5] because they have two main critical points: (1) they risk conveying the wrong message, namely that the reconstruction is the truth instead of one of the possible interpretations of the past; (2) they risk becoming a \"black box\" [6] (p. 105) where the sources and interpretative reasoning are not declared nor available both to the scientific community and to users. Despite prudence and criticisms, many benefits have been considered by the scientific community, considering virtual reconstruction as not just a mere visualisation but as a scientific tool with great cognitive value, since it facilitates the management and understanding of complex information thanks to 3D simulations [7, 8, 9]. After years of scientific debates, the introduction of internationally valid principles about the computer-based visualisation of Cultural Heritage (London Charter and Principles of Sevilla), have effectively oriented the scientific discussion with the aim of overcoming the initial concerns [10, 11]. Following these regulations, virtual reconstructions are designed following accurate workflow of analysis and interpretation of data and results are no longer presented as peremptory. However, the question of data management remains open. Although imprecision and subjectivity are mitigated using structured metadata and paradata [12], these are not always easily accessible outside the research laboratories. Furthermore, there are not yet universally accepted methods and tools to manage data and paradata and to display uncertainty and conflicting or alternative 3D reconstructions [13]. The five-step method presented in this article is conceived to overcome such issues and use a 3D simulation tool based on the Extended Matrix (EM) [14; 15], to answer precise archaeological questions that could arise during the analysis, synthesis and interpretation of a site. EM is a visual node-based formal language grounded on a stratigraphic approach designed for virtual archaeology and on the theory of knowledge graphs. The term \"extended\" highlights that it includes and defines not only archaeological stratifications (SU) but also their hypothetical reconstructions (Virtual Stratigraphic Unit--USV, see Figure 1). Given that, within a EM standardised \"five steps\" methodology, it is possible to account, using a graph database connected to a 3D environment, all the relevant sources (data) and the logical-interpretative processes of analysis and synthesis (paradata) that have led from archaeological evidence to the reconstructive hypothesis. The EM approach is part of a more general trend towards information management based on knowledge networks (graphs) expressed through data triplets (node, arc, node), oriented to convey the interconnection between the elements, and recorded within a graph database [16]. Although international standards in the Cultural Heritage domain such as CIDOC-CRM or operational tools such as the Matrix are based on information triplets, graph databases are still poorly adopted in favour of \"traditional\" table-based databases. Thus, an EM is a knowledge graph intended to explicitly represent properties like the chronological extension by means of graphical conventions (y axis = time, black lines = stratigraphic relations, dotted lines = data provenance, etc.). In recent years, several case studies [17; 18; 19; 20; 21; 22; 23] have used the Extended Matrix methodology offering important test-beds to validate the theoretical framework (EM, [14]), the formal tools (USVs [14], proxies [15]), and its digital ecosystem framework (Extended Matrix Framework--EMF [15]). Section 2 offers the result of this process of maturation as a standardised five step process that, in turn, allows to address several main issues related to the virtual reconstruction process as in Section 3 will be discussed.