## 5 Proof of Concept  
The presented concept of toolchains and its implementation in the BIMSWARM platform with the integration of the openCDE-compliant web interface is demonstrated in the following proof of concept. A use case is defined for the planning, tendering, and execution of a maintenance task by a building operator. The schematic representation in Figure 9 shows the basic structure of the use case performing seven activities in four different IT products. The data exchange between the IT products is identified and modeled with particular format types. This maintenance task is defined in the Facility Management (FM)-system (Figure 9a). The order for the maintenance task is generated and transferred using the GAEB DA XML file format to a software application for model-based tendering (Figure 9c. In parallel, the respective IFC file is transferred from the CDE (Figure 9b) into the model-based tendering software. The order is filled with the description and pricing of the maintenance works to create a bill of quantity within the tendering software. Meanwhile, the tendering process takes place, and a craftsman awards the contract for the order. The work items from the bill of quantity are linked to the entities of the IFC model end exchanged in an ICDD container back into the FM-system (Figure 9d) and the CDE for long-term storage. The maintenance tasks are generated as BCF issues in the FM-system based on the linked IFC entities from the ICDD and transferred to the contractor in a facility service app (Figure 9e). After maintenance works are finished, the contractor returns the BCF issues back to the  
Figure 9: Schematic representation of the use case maintenance task of a building operation stakeholder. FM-system (Figure 9f) and the CDE (Figure 9g). The status of the maintenance works in the FM-system is updated, and the BCF issues are stored in the CDE to archive the changes related to the building model. For modeling the toolchain based on the provided use case, the product-type groups FM-operator system, CDE, tendering, awarding, accounting (TAA), and facility service app are used. Having the use case, in the next step, the user can model the toolchain in the Composer (see Figure 10) on an empty canvas. Activities and contents can be modeled using drag-and-drop on the elements from the toolbox in the top-left corner of the canvas. The process flow and data flow can directly be created after placing the activities. Metadata of the toolchain or the toolchain items can be edited. The graphical user interface of the Composer enables to specify the activities from the schematic flow as activities or product type groups and, in the next step, to select particular construction IT products from the BIMSWARM marketplace for the activities. The particular software products chosen for the activities are displayed by their logos and names. Forks and joins are modeled as well per drag and drop. The Composer checks during modeling whether the process flow and the data flow are modeled correctly. The compatibility check based on the data formats to be transferred between the toolchain items is implemented only prototypically so far, but will be implemented into the Composer in the further development. Based on the defined toolchain, multiple instances of the toolchain can now be created as required, so that the use case can also be executed multiple times in parallel. The products used within the toolchain can interact with the BIMSWARM platform and execute the workflow as shown in the Sections 4.2 and 4.5. For each data object modeled in the toolchain, a content object in the respective information container in the openCDE-compliant data storage is automatically created. After creating and executing the toolchain in the Composer (see Figure 10), the JSON Object presented in Listing A1 is produced using the query 1 from Figure 8. The JSON Object is built regarding the UML diagram in Figure 4 and comprises general information about the toolchain, such as the creator or descriptive metadata.