## 5 Conclusions and Future Works  
In this work, we present a system proposal that exploits the public Blockchain concepts in combination with those of the BIM, IoT and SSI to ensure the eligibility, transparency and traceability of the entire life cycle of a building artifact. We are working to its implementation by a decentralized application, designed and implemented following the so called Agile Block Chain Dapp Engineering (ABCDE) method [41]. In Figure 7, the class diagram that describes the model proposal is shown. Figure 7: Class diagram of the whole system proposal. The DID class describes all system entities, representing them with an Ethereum address. It models all stakeholders, hence all interested parties, that is, any person, group or entity that may be affected by a decision or changes during the life cycle of a building, including the building itself. So, in the model proposal, buildings are modeled through DIDs, and the IoT devices, appropriately placed in the building under construction or finished are modeled as DID delegates and are identified by an Ethereum address. The entire logic that allows entities to interact among them is implemented from the Information Management Platform. This platform includes all smart contracts, servers, and the user interfaces for a friendly information management. The proposal is designed to exploit the Veramo project, which stems from the uPort project that was split into two projects, Serto and Veramo. Both projects carry on the mission of decentralizing the internet and returning control of their data to individuals. In this work, innovative technologies allow the development of a system for the efficient management of digital identities related to natural persons, organizations, or things, in our case building artifacts. All these digital identities can independently manage their claims/attributes also through zero knowledge proof algorithms, deciding from time to time which ones to share and with whom. So a digital identity can be the holder of the claims--the issuer--that is, the digital identity that issues a credential--or the verifier--that is, the digital identity that verifies in real time and at any time the validity of a given credential. The proposal presents a system that must manage the storage and recovery of all claims/information, the verification of their validity and in general the information management automatically. It is an ambitious model, a novelty for international buildings, that, by exploiting the Blockchain technology together with the concepts of SSI, IoT and BIM, aims at the digitization of the construction sector, reducing not only costs, waste of time and bureaucratic complexity, but also the distance between citizens and institutions, strengthening trust in digital services and promoting their diffusion. Future work will aim to investigate in detail the notarization of the work flow in the so called CDE. The British technical legislation has proposed an organic structuring of the CDE with the definition of four areas: \"Work in Progress\", \"Shared\", \"Published Documentation\" and \"Archive\" (ref. [[https://bimportal.scottishfuturestr.org.uk/level2/stage/1/task/22/overview-of-the-common-data-environment-cde](https://bimportal.scottishfuturestr.org.uk/level2/stage/1/task/22/overview-of-the-common-data-environment-cde)]([https://bimportal.scottishfuturestr.org.uk/level2/stage/1/task/22/overview-of-the-common-data-environment-cde](https://bimportal.scottishfuturestr.org.uk/level2/stage/1/task/22/overview-of-the-common-data-environment-cde)) (accessed on 8 April 2022)). The transfer of information (for example, the transfer of a model or a document) from one area of the CDE to the next must take place through appropriate checks and verifications. The outcome of these checks and verifications will lead to approving or not the passage of the information to the next area. The approval procedures, therefore, are put in place to safeguard the correct flow of information.