## 7 Discussion and Outlook  
Considering a blockchain-based smart contract framework as a socio-technical system underlines the importance of social, organizational, and technical factors, as well as legal policy [2]. The integration of smart contracts into legally binding construction contracts presents a challenge due to the lack of legal precedents and regulations so far. Semi-automation seems to be a suitable compromise for offering a legally compliant and feasible solution. Construction lawyers accompany the development of the framework and ensure data security and legal compliance. An important issue to deal with is the immutability of the blockchain and the resulting advantages and disadvantages. Storing an immutable copy of the contract in the blockchain can prove beneficial for both parties, as it can prevent disputes about the individual terms of the contract. Furthermore, the immutable copy of the contract can serve as evidence in court. On the other hand, data protection concerns arise whenever personal data are to be stored without the possibility of erasing them. The system needs to be implemented in a way in which General Data Protection Regulation (GDPR) requirements are fulfilled and privacy is preserved. This problem can be mitigated from the start if as few personal data as possible are stored on the blockchain. This supports the idea of preserving privacy within the system by storing all critical files (such as legal contracts, invoices, personal data of participants, and bank details) in a CDE but having a hash value on the blockchain to prove authenticity. The security and confidentiality of transaction information are provided through the proposed use of a private consortium blockchain. The immutability feature is considered a shortcoming considering the frequent changes and revisions in construction projects [3]. Changes in the contractually agreed scope might require the addition or removal of certain work steps, resulting in an update of the BoQ or the billing plan. The subsequent modification of billing arrangements is also possible if, for example, an additional agreement concerning partial payment needs to be concluded. Figure 12: Smart contract execution in the Blockchain Explorer. Furthermore, global changes that affect the BIM are not rare either, and the implementation of change order management is therefore needed. The BIMcontracts concept provides flexibility through the versioning of the BCC stored in a CDE and, thereby, of its internal files that are affected by the changes. Since these changes are an amendment of the original contract, both contracting parties should sign a new smart contract confirming the agreement on the update. The new hash values of the container and the internal files are calculated and saved within the new smart contract. Since the internal files are stored in a CDE, any changes during the construction project are tracked. Change order management is one of the ongoing implementation steps, and it will be addressed in more detail in future research. The same applies to the implementation of model-based reporting and defect management. As the framework relies on interoperability and openBIM standards and formats, the integration and extension of the BIM Collaboration Format (BCF) are foreseen at this point. This vendor-neutral interface plays an important role in structured project coordination and interdisciplinary collaboration. It allows for the communication of IFC-based issues and openBIM processes and can support use cases in the construction and operation phases. Certainly, the concept can also be further developed in terms of the final account, different types of construction contracts, and the complexity of the use cases and smart contracts. Since complex scenarios are also possible, e.g., some events can also depend on the status of other billing units or even smart contracts with other subcontractors. The chaining of contractual relationships is an important issue for ongoing enhancement.