# Ontology-Based Representation and Reasoning in Building Construction Cost Estimation in China
## 1 Introduction  
Cost estimation is one of the critical tasks for participants in the AEC/FM (Architecture, Engineering, Construction, and Facilities Management) industry. However, in practice, estimators still have to extract useful information from printed design drawings or CAD drawings manually or rebuild three-dimensional models of cost estimation manually [1; 2]. The process of manual work, which is time-consuming, lacking in efficiency, and prone to error, still depends on the estimator's knowledge and experience, and the design results cannot be used directly due to the subjectivity that results from the cost estimator's knowledge and experience.  
BIM (Building Information Modeling) technology provides a potential solution to generate takeoffs, counts, and measurements directly from a unique and continuously updated model [1; 2]. BIM supports the entire project lifecycle and has the capability to integrate costing efforts throughout all project phases [2]. Compared to traditional methods, all of the cost estimation information can be shared directly with the support of open data exchange standards for BIM, such as IFC (Information Foundation Classes) [3], which can avoid heavy human workload, subjectivity, and manual errors. At present, several BIM-based cost estimation software applications [4; 5] have been developed to improve the efficiency and accuracy of estimation. However, these software applications rarely support the IFC standard, which is the most comprehensive data exchange standard for BIM. Moreover, thereare differences between the specifications of different regions for cost estimation, and these applications can hardly be used in actual projects in China.  
Several studies have revealed that cost estimation work has mainly focused on the schematic design or tendering phase. [PERSON] et al. [1] developed a program of cost estimation for tendering based on BIM, and [PERSON] et al. [6] presented an ontology to represent estimators' rationale regarding the features relating building product models to construction cost. [PERSON] et al. [7] gained detailed information through the use of cost estimation based on BIM and ontology, such as the specific material and construction type. However, these studies are mainly concentrated on the design or tendering stage, and do not consider the project lifecycle. Although the cost estimation based on the BIM model is more efficient and accurate than the traditional methods, the intervention of the cost estimator's subjective decisions and semantic ambiguity is inevitable in determining costs [1; 7].  
In dealing with the current cost estimation issues in the building construction industry, it is necessary to use a proactive approach rather than a reactive one. Thus, to solve the above problems, this research introduces the notion of ontology into cost estimation, and the built ontology model can be used in various phases of the project lifecycle. In this way, cost estimation ontology supports the extension or modification of knowledge and rules from the perspective of pure cost estimation rather than software implementation, thereby enhancing the extendibility of BIM-based cost estimation software for different specifications.  
This research is organized as follows. The research background is outlined in Section 1. Section 2 provides a brief review of related studies. The cost estimation ontology is proposed in Section 3. Section 4, which is based on a cost estimation ontology, discusses the implementation of building construction cost estimation, and in Section 5, the proposed approach is illustrated with cost estimation examples, and a process of cost estimation is discussed. Finally, conclusions are drawn in Section 6.