# An open-BIM Approach to IoT Integration with Incomplete As-Built Data
## 3 The Proposed Openbim Methodology
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Method** & **Advantages** & **Drawbacks** \\ \hline \multirow{4}{*}{**Semantic web approach:**} & \(\bullet\) & Linking data silos; & \(\bullet\) & Need to represent data in \\  & \(\bullet\) & managing cross-domain & \(\bullet\) & homogeneous format (RDF); \\  & for storing, sharing, using & information; & \(\bullet\) & RDF is not optimal for querying \\  & heterogeneous data [44; 45]. & \(\bullet\) & effective in projects with & dynamic data; \\  & & broad scope. & \(\bullet\) & data redundancy risk; \\  & & & \(\bullet\) & fix structure and storage consuming. \\ \hline \multirow{4}{*}{**Hybrid approach: semantic web + relational database:** both approaches are used for storing cross-domain data [46; 47]. & \(\bullet\) & Data is stored in the most suitable platform; \\  & & & \(\bullet\) & time saving (no conversion); \\  & & & \(\bullet\) & storage saving; \\  & & & \(\bullet\) & better performance; \\  & & & \(\bullet\) & effective QL. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Eventually, buildings' performance can be simulated under known building systems organisation using individual asset components. For instance, for the anomaly diagnosis of Heating, Ventilation and Air-Conditioning (HVAC) systems in a specific building, only the basic mechanical system information is needed: describing the HVAC system configuration and the links between architecture zones and HVAC terminal units [51]. This scenario is used in Section 4 for demonstrating the benefits of the proposed approach. In the development of the IfcAsset, in fact, the classification system adopted by asset and facility managers must be considered in order to support inter-operable and flexible AM processes. For querying and modifying the IFC, several Application Programming Interfaces (APIs) can be used. The IfcOpenShell-python ([[http://ifcopenshell.org/](http://ifcopenshell.org/)]([http://ifcopenshell.org/](http://ifcopenshell.org/))) module and the BIMserver ([[https://github.com/opensourceBIM/BIMserver](https://github.com/opensourceBIM/BIMserver)]([https://github.com/opensourceBIM/BIMserver](https://github.com/opensourceBIM/BIMserver))) software for IFC visualisation and queries are used in this research. Figure 2 depicts the proposed methodology. The process starts with the definition of IRs, which is designed to identify the relevant data employed for the operation of the building according to the business and client needs and the outcomes of the application. This step is composed of three sub-tasks regarding the definition of the static and dynamic IRs and the definition of the Service Level Agreements (SLAs).The static IRs correspond to the AM information, characterised by a low frequency of updates and more classical information management. Static IRs include the level of aggregation of the assets (granularity) at which the maintenance interventions are conducted. The dynamic IRs concern the IoT data management, including how to aggregate data into indicators to measure performance through the installed sensors, and how to associate this information with the physical  
Figure 1: IfcAsset schema. and spatial elements of the building. The SLAs concern the performance agreed for operating the assets at an acceptable service level. The IRs definition step is crucial to the IFC processing and the creation of the IfcAsset assignment relationships. The IFC processing should consider the classification system used for AM (explicitly related to how the static and dynamic data are handled). This would facilitate the adoption of the methodology in practice and increase its usability. The next step is IFC data processing to meet the IRs. To achieve this, it is necessary to edit the initial IFC file generated through the BIM authoring software. IoT integration requires access to data schemes related to objects that might not be available (modelled) in the IFC file.