# Ontology-Based Representation and Reasoning in Building Construction Cost Estimation in China
## 3 The Building Cost Estimation Ontology Model
### Ontology Representation Model
#### 3.1.1 Concept Model Ontology  
The \"Code of Valuation with Bill Quantity of Construction Works (Chinese standard number GB 50500-2013)\" (GB 50500, hereafter) [36] is a Chinese national specification for cost estimation, and provides the unified rules for classifying and determining the bill quantity items by means of the bill quantity method. It defines a classification system similar to MasterFormat [37] for classifying construction products into cost items and provides many quantity takeoff rules for calculating the quantity takeoff for cost items [1]. MasterFormat, a publication of CSI (Construction Specifications Institute) and CSC (Construction Specifications Canada), is a master list of numbers and titles that  
Figure 1: Steps for ontology representation model interpretation. are classified by work results. Thus, this research takes the GB 50500 specification as the main reference specification. The concept model ontology leverages ontological modeling to model cost estimation concepts and the relationships among these concepts, which are extracted from building specifications, construction documents, and BIM data. By analyzing the relationships between concepts, reasoning rules are defined. In the reasoning procedure, the concepts are selected to represent a list of potential conditions that must be considered in the cost estimation. These concepts are hierarchical, and the semantic relationships among them are organized to benefit the reasoning by identifying the reasoning rules. According to the characteristics of building construction cost estimation, this research proposes the following two steps to build the concept model ontology. Step 1: Concept taxonomical structure and hierarchy. The first step is to define the related concept taxonomical structure and hierarchy for building construction cost estimation. Based on previous studies, combined with the characteristics of cost estimation in China, four primary classes, i.e., project classifications, building products, building features, and cost items, are defined as the cost estimation concept model ontology. Through the defined properties of the primary classes, the concepts of each class can be further categorized. Here are the steps to define these primary classes in this research:  
1. Project Classification  
GB 50500, published in 2013, divides construction engineering into subsection projects, subentry projects based on measurability and project valuation. GB 50500 defines hundreds of cost items for classifying all product concepts of the AEC and MEP (Mechanical/Electrical/Plumbing) industry in a building project. This specification meets the requirements of cost estimation in China and is taken as the main resource for extracting project classification concepts. Thus, GB 50500 is well-suited for project classification to represent its semantic properties, including monomial projects, unit projects, subsection projects, and subentry projects, and the relationship is shown in Figure 2. GB 50500 has a better classification hierarchy and clearer categorical attributes. UNIFORMAT II [38], a classification standard of ASTM (American Society for Testing and Materials) Standard E 1557-05 (the standard was revised in 2005 and represented as E1557-05), is a format for classifying building elements and related site work. Elements usually perform a given function, regardless of the design specification, construction method, or material used. UNIFORMAT II is a significant advance over the original UNIFORMAT classification in that it has added elements and expanded the descriptions of many existing elements [38]. Hence, UNIFORMAT II is chosen as the hierarchical reference for project classifications of the concept model ontology. Figure 2: Example of the concept representation of project classifications. 2. Building Product  
The classification of OmniClass Construction Classification System (known as OmniClass or OCCS, US) [39] is used as the secondary class to further represent concepts in the concept model ontology.