# Generic Language for Partial Model Extraction from an IFC Model Based on Selection Set
## 7 Conclusions  
A building project always consists of different types of information from multiple disciplines. However, business tasks require only a part of the complete building information model. Meanwhile, the required information varies depending on business tasks. A common method for partial model extraction which meets user-defined extraction requirements is necessary. For this purpose, a generic language for partial model extraction based on the Selection Set was proposed to extract a partial model from the IFC model. The Selection Set was designed to represent extraction requirements. Elements in the Selection Set work as input parameters of the partial model extraction method. Due to the complexity of requirements for business tasks, several extraction requirements could be defined in the intersection or union form. Furthermore, seven rules were defined to extract the partial model based on mathematical logic and set theory. These proposed rules ensure the syntactical and semantic validity of the partial IFC model during the extraction process. Firstly, the proposed method queries IFC data which matches the requirements defined in the Selection Set, such as IFC entities, properties, and relations. Subsequently, according to seven rules for partial model extraction, these extracted IFC data are defined as the nodes to query other related IFC data, and redundant information is filtered for forming a valid partial model. Considering the processability of the computer and the readability of users, the XML schema was adopted to design the generic language for partial model extraction. Given the definitions of building information in the IFC schema, this study developed a mapping between IFC data and the elements defined in the PMESS method, which could meet diverse requirements defined by users. Through the PMESS method, users can extract the required information from the original model under different extraction requirements, such as objects, properties, and relations. In addition, the PMESS-based configuration file can be saved as a common template for reuse, which improves the efficiency of the definitions of extraction requirements. To demonstrate the feasibility of the proposed method, a practical project was used to extract different partial models under three conditions: object types, object relations, and specific rules. Figure 11: Partial models of curtain walls in different placements. Compared with the original model, the required objects were correctly extracted, which showed the validity of partial models at the semantic level. Furthermore, the extracted partial models could be imported back into the original software tool, which demonstrated the syntactical validity of the extracted IFC file. Currently, although some commercial software products can be used to extract the required objects, it needs users to manually select the required objects, and the partial model cannot be extracted according to the particular rules. Some researchers have carried out research projects for partial model extraction, and mainly focus on some specific information, such as geometric information. In this study, the proposed PMESS method makes users automatically extract the partial model by requirement definition. Furthermore, users can define different requirements to extract the required partial model based on the PMESS, which can accommodate more applications. This study is an important step in data sharing and exchange of building projects, and it also has room for improvement. For example, bSI proposed IDM and MVD for exchange requirements, and defined several templates for practical tasks. To extend the applicability of the proposed method, the PMESS should be mapped to IDM and MVD. Given the fact that the PMESS was designed based on the XML schema, the mapping mechanism between the PMESS and mvdXML could be further studied. Conceptualization, X.D. and H.L. ; Methodology, X.D. and H.L. ; Validation, H.L., J.X., and Y.Z. ; Writing--original draft preparation, X.D. and H.L.