# Ontology-Based Representation and Reasoning in Building Construction Cost Estimation in China
## 3 The Building Cost Estimation Ontology Model
### Ontology Representation Model
#### 3.1.3 Construction Condition Ontology  
Mapping is required between the ontologies of work items and construction conditions to realize an information description of a construction condition's subcategory and subsection by means of the work item. To automate the mapping reasoning, this research proposes a construction condition ontology that consists of the specific classes that are used to select work items. Estimators select a  
Figure 4: Framework of the work item ontology. Figure 5: Part of the GR ontology. work item that is suitable for the construction condition using a reasoning rule based on the expert's experience (e.g., the construction condition of earth excavation in foundation pit engineering involves the work items of excavator, construction sequence, earthwork transportation). Construction condition can be extracted from BIM, the specifications of cost estimation, or historical data. In the process of cost estimation, all specialized data concerning work items may come from suppliers and/or BIM; for example, cost-related information about a specific material can be found in the resources of the work item ontology or in the documents provided by the supplier. The construction condition ontology, extracted from IFC and documents, is used to recognize BIM data and knowledge items and is converted into RDF(S)/OWL format. Knowledge item is a unit of knowledge; a knowledge item is the physical or symbolic manifestation of such knowledge. For example, a \"schedule plan document\" is the manifestation of the \"schedule plan\". Knowledge item includes documents, CAD drawings, roles, records, reports, knowledge classifications, and communities of common interest in construction cost estimation [45; 47]. The information required for the cost estimation ontology has different sources, so effective heterogeneous information integration is an important issue. The goal of the Semantic Web is to provide tools that make it easier to integrate information across all formats, representations and schemas. RDF provides a flexible and extensible data model that eases the task of combining data sets into a common data model [48]. Because the machine cannot interpret the meaning of the XML (Extensible Markup Language) and IFCXML data exactly, the data need to be converted into machine-readable form by using XSLT (Extensible Style-sheet Language Transformations). XSLT [49] can solve the problem of integrating heterogeneous data sources. XSLT is a language for transforming XML documents into other XML documents. A special advantage of this approach is that, although XSLT is written independent of any programming language, it can be executed by a program written in almost any up-to-date programming language [50]. Hence, source data can be converted into RDF data via the XML to RDF transformation engine of XSLT. RDF data can be expressed as a triple structure, that is, resource, attribute, and attribute value. The approach is capable of representing meaning of information both by concept and by ontology relationship. The data source transformation process is, however, outside the scope of this research. Semantic Disambiguation  
In practice, differences in language, personal habits, cultures, and customs have resulted in different description forms of concepts in cost estimation. For the same concept, different classification methods may have different expressions, such as abbreviations and synonyms. Particularly in China, semantic problems are more prominent due to the multiplicity of national cultures. Consider \"?E+?\" and \"?E+?\" or \"?E+\" and \"?E+\"; the two pairs of concept have the same meanings, of earth excavation and concrete, respectively, in Chinese, so it is difficult for the estimator to address the problem of semantic disambiguation. To solve this problem, the ISO committee has proposed IFD (International Framework for Dictionaries) [51] to allow all of the information in IFC format to be tagged with a Globally Unique ID (GUID). However, the framework lacks cost estimation information.