## 4 The System Proposal: An Introduction
### ABCDE Method: Goal and Actors  
The goal of the system proposal is the digitization of the building sector, exploiting, in addition to BIM, IoT and to Blockchain, the concepts of the new identity management model based on SSI, to contain the risk of fraud, manipulation and corruption, and favor the transparency and verifiability of information related to a building artifact during all its life cycle. The proposed system is the result of the integration of three different subsystems, each with their own actors and features:  
1. Blockchain subsystem: it provides a decentralized infrastructure based on Smart Contracts for managing information relating to a building product throughout its life cycle;
2. IoT device subsystem: system of IoT devices for structural monitoring, for monitoring all systems, electrical, photovoltaic, heating, or for example for monitoring the presence of people or things;
3. Information management platform: web platform that allows authorized users to access information relating to a given building, verify its validity and upload documentation. Regarding the actors of the system, they are who interact with the system. They can play human roles but also devices and external systems. Actors are outside the system. They interact with it, initiate the use case activity, provide input to it, and/or receive outputs from it. So, for example, a timer that triggers an action is an actor, a smart contract that interacts with the dApp is an actor. Figure 2: (**a**) Traditional Process of verification and (**b**) Process of verification in SSI system. The actors of the system are listed below. 1. System administrator is the one who carries out the deployment on the Blockchain of the contracts used by all users and initializes the system;
2. DIDs are Decentralized IDentifiers representing building artifacts, and users/ stakeholders. They have an owner, whose address can also be replaced by the address of a multi-signature contract, which activates the execution of certain actions only with the multiple signatures, therefore with the approval of multiple users. This functionality will be used in our system by DIDs representing building artifacts. Stakeholders can be Architects / Engineers / Safety Managers / Managers of public bodies. They are the people or companies, identified through a DID in our case an Ethereum address, who use the platform to acquire a document, to notarize a document or to verify the validity of a document;
3. Smart Contracts are the only actors who interact directly with the Blockchain. They are the smart contracts that implement the application logic of the system. For the implementation of the smart contracts listed refer to [[https://eips.ethereum.org/EIPS/eip-1056](https://eips.ethereum.org/EIPS/eip-1056)]([https://eips.ethereum.org/EIPS/eip-1056](https://eips.ethereum.org/EIPS/eip-1056)), [[https://github.com/ethereum/EIPS/issues/780](https://github.com/ethereum/EIPS/issues/780)]([https://github.com/ethereum/EIPS/issues/780](https://github.com/ethereum/EIPS/issues/780)), [[https://docs.soliditylang.org/en/v0.8.4/solidity-by-example.html](https://docs.soliditylang.org/en/v0.8.4/solidity-by-example.html)]([https://docs.soliditylang.org/en/v0.8.4/solidity-by-example.html](https://docs.soliditylang.org/en/v0.8.4/solidity-by-example.html)), and [[https://solidity-by-example.org/app/multi-sig-wallet/](https://solidity-by-example.org/app/multi-sig-wallet/)]([https://solidity-by-example.org/app/multi-sig-wallet/](https://solidity-by-example.org/app/multi-sig-wallet/)) (accessed on 8 April 2022); 1. The _EthereumDIDRegistry.sol_ contract tracks all DIDs; 2. The _EthereumClaimsRegistry.sol_ contract tracks all claims/certificates of DIDs that identify the building artifacts; 3. The _Verifier.sol_ contract implements the logic for verifying the validity of building artifacts certifications; 4. The _MultiSignWallet.sol_ contract implements the logic for multiple approval of a given on-chain transaction;
4.