## 1 Introduction
Through the SSI paradigm, two entities (digital identities) can exchange data with each other, trace the entities behind the digital identities involved in the data exchange thanks to the so-called decentralized identifiers (DIDs) and DID documents, and verify the validity of the exchanged data. The proposed model includes a decentralized application (dApp) for the notarization of the information flow in common data environments (CDEs). The dApp notarizes on-chain the information flow relating to a given job order (precisely relating to a design commission in the proposed system and, henceforth, simply commission) within a CDE, i.e., the space on a server in which data and files related to a specific commission are stored. Specifically, it is made up of two subsystems: one on-chain and another off-chain. The on-chain subsystem consists of the smart contract, which implements the logic for notarizing the information flow within a CDE and for triggering the passage from one area of the CDE to the next thanks to the events emission. The off-chain subsystem consists of an application that includes the software that calculates the hash of the content of the information to be notarized, the server side software, which listens to the events issued by the contract to trigger the automatic transfer of contents from one area of the CDE to the next when the contractual conditions implemented in the smart contract are all respected, and the graphic user interface (GUI), which allows users to interact with the on-chain subsystem. Note that, to date, there are no CDEs that implement APIs for managing the automatic transfer of contents in response to external triggers. For this reason, in this article, only the complete implementation of the on-chain system and the latter and former application of the off-chain subsystem are presented. (As of today, there are no APIs for this interaction, but there are several initiatives moving in this direction. For example, Harpacas and Chainplug--the former being a leader in the software market for large construction and the second being an innovator in the field of blockchain technology for workflow automation--have started a collaboration with the aim of offering digital and complete technological solutions based on BIM and blockchain for the construction market [4]. )Differently from the proposed model, [PERSON] et al. and [PERSON] et al. [6; 7] proposed blockchain-IPFS-based solutions for document sharing and version control without the involvement of a centralized third party, and [PERSON] et al. [23] presented a proof of concept based on blockchain technology for the certification of information flow between CDEs in applications related to structural design. Regarding digital identities and, precisely, digital identities of things such as IoT devices and buildings, [PERSON] et al. [24] discussed the benefits of SSIs in CI and presented a blockchain-based model for notarizing and certifying the information related to a building without entering into the details of the notarization of data flow in CDEs, as this article does. In [24], the authors present a decentralized system based on the Ethereum blockchain that manages the information associated with a building and is generated by stakeholders, natural or legal entities and IoT devices. In this system, stakeholders and buildings are identified through their DIDs, and the storage of all building information is managed both through a centralized database and blockchain. [PERSON] et al. [25] and [PERSON] et al. [26] investigated and proposed SSI-blockchain-based approaches for IoT devices. Precisely, [PERSON] et al. presented a platform, named the Know Your IoT device platform (KYoT), that leverages the ERC 734 and 735 standards of the Ethereum blockchain for SSI (now dated) and the SRAM-based physically unclonable functions (PUFs) of these devices for the identification of Arduino devices within IoT networks such as networks for supply chain tracing and IoT data marketplaces. [PERSON] et al.