## 3 Requirements Analysis  
The research gap is identified from the literature review as the lack of vendor-neutral interoperability [4; 23; 24] and the need for structured and systematically formalized workflows [18; 23]. Moreover, the collaboration between stakeholders focuses on centralized document-based data [5; 40], while there is a gap in exchanging information that is decentralized and asynchronous in federated resources [40; 42]. Altogether, the construction industry is approaching web applications and web technologies for information exchange [5; 6; 7] as well as platform ecosystems for BIM collaboration [15; 43]. Considering the research gaps and research directions, an analysis of the current user requirements regarding information exchange workflows was conducted. For this purpose, the involved user groups of the toolchain framework were identified. Prior to the identification of technical requirements, challenges in project collaboration and user-centered requirements for interoperable model-based BIM workflows were identified in workshops with experts from the construction industry. Therefore, several use cases were defined systematically in templates based on the methodology proposed in [44]. These use cases are comprised of three characteristic application scenarios along the building life cycle: (1) model checking regarding the employers information requirements (EIR); (2) model-based cost-estimation; and (3) the legally compliant commissioning of a building. These application scenarios are then decomposed into individual workflows and specified for use in the toolchain framework according to the use case templates and accompanying BPMN diagrams. The developed use cases were presented and evaluated by the project partners as well as by other experts from the AECO industry and were used for the concept development of the toolchain framework. For any further workflows, expert knowledge is supposed to be used for generating further toolchains or for refining the granularity of existing toolchains. In order to face the identified challenges of the non-formalized process implementation, the consideration of various standards and the combination of software from several vendors, subsequent ideation was started to examine the current state of collaboration more intensively. Considering the standardized method of IDM for formalizing BIM workflows and information exchange (c.f. Section 2), stakeholders in construction projects establish collaboration utilizing BPMN. To directly integrate software products into these workflows, structures are needed that map the interaction of corresponding applications from BPMN and control the underlying processes via a central platform. These structures are called toolchains. A toolchain is defined as a linkage of software products to common workflows (c.f. Section 1). The term software product subsumes applications, services and content within the presented service infrastructure, with which holistic digital value chains for BIM-based planning, construction, execution and operation can be created. To ensure the error-free linking of software products, a data model for software products is required that maps all relevant information for such a product. In addition to the versioning of the product, this also includes detailed descriptions of all functions that are offered and the supported import and export formats. A uniform description format is required, especially for the recording of software product functions to enable clear comparability of different software products. Depending on the level of detail of the collected data, an automatic compatibility check can also be performed when creating a toolchain. The workflow mapped in a toolchain should be available within the platform as an executable process. For this purpose, a concept must be developed which represents the communication of the individual components in relation to the process flow. Therefore, a status model is needed to map the process flow.