# Ontology Construction of Digitization Domain for Ancient Architecture
## 3 Ontology Construction in the Digitization Domain of Ancient Architecture  
### Classification and Expression of Concepts  
In the context of an ontology model, the establishment of a conceptual layer represents a crucial step in the ontology development process. By employing a multi-level division and expression of concepts, the ontology can facilitate the construction of more comprehensive semantic spatial information and increase the reuse rate of the ontology. In the digitization ontology design of ancient architecture, this article synthesizes the general digitization workflow of ancient architecture and divides it into four technical specification steps. First, the preparatory work is carried out, including site exploration, data collection and program formulation. Then, data collection is carried out; various data devices are used, such as UAVs, 3D laser scanners, total stations, and so on. Different types of data (point cloud, image, and archive) are collected, then the point cloud data, image data, and archive data are processed. Finally, the result data are output in formats such as a three-dimensional model, an orthorectified image, digital documents, etc., as shown in Figure 2.  
In addition, based on a large number of existing literature and engineering cases related to the digitalization of ancient architecture. The digitization knowledge of ancient architecture is classified into four main categories: the digitization object of ancient architecture, the digitization technology of ancient architecture, the digitization equipment of ancient architecture, and the digitization specification of ancient architecture. Furthermore, on this basis, the concept of ancient architecture digitization ontology is divided into four levels, and the conceptual ontology framework of the ancient architecture digitization domain knowledge is constructed in more detail as shown in Figure 3.  
Figure 2: Digitization flow and frame diagram of ancient architecture. Among them, the digitization objects of ancient architecture refer to the key components that need to be preserved in the digitization work and the associated cultural relics of important value. This article primarily addresses the topic of ancient wooden structures, with a particular focus on the _Yingzao Fashi_[22], which categorizes digitization objects into five secondary conceptual categories: stonework, carpentry, tilework, carving, and color painting. The digitization technology of ancient architecture is defined as the technical methods involved in the digitization process. In recent years, there has been remarkable progress in the field, with the emergence of numerous methodologies. In accordance with the digitization workflow and the substantial corpus of literature, this article classifies the digitization technology of ancient buildings into three secondary categories: data acquisition technology, data processing technology, and data storage technology. The digitization equipment of ancient buildings is a necessary tool for data acquisition. By summarizing and sorting the equipment available on the market has led to the delineation of three secondary categories of digitization equipment: unmanned aerial vehicles (UAV), total stations, digital cameras, and three-dimensional (3D) laser scanners. The digitization specification of ancient architecture is used to describe the technical requirements that must be met in order to digitally document and preserve ancient structures. The aforementioned categories are further subdivided into two secondary categories: national standards and local standards. In order to provide the most comprehensive description of the research object, this article divides some of the conceptual classes into three and four levels, respectively. For example, the second-level carvings are divided into three third levels: wood carvings, clay sculptures, and stone carvings. Among these, wood carvings are further divided into two fourth levels: craft wood carvings and art wood carvings.