# An open-BIM Approach to IoT Integration with Incomplete As-Built Data
## 3 The Proposed Openbim Methodology  
In this section the methods employed to develop the proposed openBIM approach for IoT data integration are presented while exposing the limitations. Then, the proposed workflow is depicted addressing these limitations to leverage the full potential of the available static and dynamic data, supporting the development of AM applications, even when as-built data is incomplete. The purpose is to create an approach that is effective when dealing with existing buildings where as-built information is frequently absent or not reliable. The proposed openBIM approach aims to extend the BIM methods and tools for improved accessibility, usability, management and sustainability of data in AECO [21]. It promotes data sharing and collaboration among parties using open standards, addressing the common BIM issues related to proprietary technologies and software. For this purpose, the Industry Foundation Classes (IFC) data schema has been adopted to support and handle the BIM data [48]. The IFC schema is an object-oriented open standard [49] widely studied as an effective means for interoperability, sharing, collaboration and classification. The IFC schema is extensive and complex, and therefore its usage has been limited to simple software interoperability workflows and visualisation of key information of the BIM model. Nonetheless, IFC offers good support for not only geometry representation, but also semantic data enrichment. In this research, the IfcSharedFacilitiesElements schema has been employed to handle geometric and semantic information of both existing and newly created IFC objects, supporting real-time data integration. Rarely, the level of both geometric and semantic detail and the classification system (the granularity) adopted in developing the BIM model, in the design and construction phase, is adopted in the use phase. According to [50], the IfcAsset has been adopted for re-aggregating building components in order to achieve the desired level of granularity used in AM. The IfcAsset (the element breakdown is elaborated in Figure 1) is defined as \"a grouping of elements acting as a single element that has a financial value\", allowing objects that are not spatially connected to be related, through the relationship IfcRelAssignSToGroup. Moreover, another artefact that can be leveraged for semantic enrichment of the BIM model is the IfcAsset, which allows the objectified relationships IfcAssignToActor, IfcAssignToControl, IfcAssignToProcess and IfcAssignToResources to be associated with a wide set of data within the context of the AM domain. In practice, as-built data is incomplete and not reliable. When integrating with IoT data, this may result in hampering an effective digital representation of both the sensor objects and the spatial elements measured by the sensors. This issue is addressed by modelling non-geometric objects in IFC, which allows a modular updating of the BIM model. This approach leverages both the 3D and semantic potential of the IFC schema, streamlining the integration of BIM, AM and IoT data. From the perspective of applications, detailed spatial/geometrical information is not always necessary. As typical distributed systems, buildings need to be monitored, managed and controlled.