## 7 Discussion and Outlook
However, this is not only a technical challenge, but also a legal one. In addition, some restrictions, such as deadline overruns, still have to be accepted to keep the complexity at a manageable level. A 5D BIM model is based on detailed scheduling of the works to be performed. The developed billing plans thus foresee the input of the completion date. Ideally, all dates can be obtained directly from the 4D schedule. Nevertheless, detailed model-based schedules are not in widespread use so far. In the presented concept, the completion date can be considered only as additional input information for the billing units, and the origin of the dates is not of critical importance. For this reason, the non-existence of detailed 4D models is not a hurdle for the use of the system. Contractual agreements of schedule objectives come with additional legal issues. Deadline overruns can trigger contractual penalties if the overrun is caused by the contractor. If, on the other hand, the overrun is not imputable to the contractor, it can constitute a hindrance, thus leading to a modification of the agreed-upon schedule. The deadline overrun should therefore be documented by the system (e.g., through automated notices of hindrance) to benefit from the tamper protection and trustlessness that the blockchain can provide. Due to the complexity of the problem, impacts from missed deadlines are not considered in the concept. However, they certainly represent an important aspect that should be investigated in the future. Cooperation among multiple parties usually causes several challenges, e.g., in agreeing on certain data exchange formats, a common location for saving data, or the permissions of each participant to view and edit these data. A well-planned technological infrastructure is crucial for efficient workflows and has a big impact on how teams collaborate. There are several existing approaches for addressing those challenges, but they are usually created by a single company, hosted on centralized cloud infrastructure, or are not suitable for critical payment processes. Especially with the idea of increasing the degree of automation and digitization in the AEC industry, it becomes clear that trust between the participants plays a big role and that the software components employed need to address this accordingly [41]. The proposed concept investigates automated payment between clients and contractors by considering smart contracts as a service ecosystem that binds to the blockchain and data storage (CDE). This contribution describes the conceptual framework and software architecture and gives a first insight into the current implementation. The concept was already presented to a wide audience consisting of general contractors, IT product providers, and subcontractors and was met with broad approval. The BIMcontracts frame work builds on the existing infrastructure and software solutions by trying to integrate the established processes as much as possible. On the other hand, where changes are necessary and improvements are possible, it tries to justify the necessity of and potential for change. This especially concerns the provision of digital BIM-based tender documents and model-based reporting. Use cases that promote collaboration are among the biggest potentials of blockchain and smart contracts alongside initiatives for enhancing transparency, traceability, and automation. Digital transformation is driven by the desire to improve and the courage to change and is merely supported by the adoption of new technologies that help to take the next step towards turning the vision into reality. Conceptualization, B.S., D.G., F.B., J.W., K.S., M.K. and X.Y. ; methodology, B.S., F.B., J.W., K.S., M.H., M.K., P.H. ([PERSON]) and X.Y. ; software, B.S., F.B., J.W., M.H., P.H. ([PERSON]), P.H. ([PERSON]) and X.Y. ; data curation, B.S., F.B., J.W., P.H. ([PERSON]), P.H. ([PERSON]) and X.Y. ; writing--original draft preparation, B.S., F.B., M.H., P.H. ([PERSON]), K.S. and X.Y. ; writing--review and editing, D.G., J.W., P.H. ([PERSON]), M.K., K.S.