## 2 An Overview
### Self Sovereign Identity and Building Artifacts  
Within the framework outlined so far, the concepts of SSI, and in particular the concepts of digital identities applied both to individuals and to building artifacts, could play a key role. The principle behind SSIs is that of digital identity managed directly by the user, and no longer digital identity centrally managed [30]. When the Internet was created, the main problem was to create a network of networks, identifying the address of the computer that is connected to the network through the TCP/IP protocol, which, however, does not allow us to trace the identity of the person, organization, or thing that uses computer. To solve this problem, several models have been introduced to identify users online. The first is the centralized model in which to create an identity it is necessary to register an account with the subject providing the online services (service provider). With this model, there is the total absence of control over the data by the person who owns the account. The next model is that of the federated identity and this is the case of SPID. In this model, a third party, the identity provider (IdP) is inserted between the service provider and the person who intends to use them. The latter has an identity (account) registered with the IdP and can use the services provided by third-party sites without having to re-register at their sites, but by logging in through the identity registered with the IdP. Also with this model, there is the absence of control over the data by the person holding the account, and it is better not to entrust the sharing of user information in a secure manner, in particular the sharing of sensitive information, such as identity documents, health data, financial data, to IdPs, such as Google or Facebook. The decentralized model based on SSIs is made possible thanks to distributed ledger technologies, in particular the Blockchain, and solves the above mentioned problems. It is not based on accounts, but it operates in the same way as real identity. There is a direct relationship with the party that must verify the so-called claims (statements) belonging to a precise digital identity. The SSI model is based on some key concepts, in particular on the concept of digital identity that can be associate both to natural or legal entity and to thing, of decentralized identifier that allows for the identification of the parties and is an address, of verifiable identifier that contains information about an entity and allows for identification and authentication of such entity, of verifiable attestations that are issued by an issuer, held by a holder and contain information, for example about attestation or authorization received, and on the concept of verifiable presentations that are created by transforming information extracted from Verifiable IDs and/or Attestations. The links among these concepts, given by the European Blockchain Partnership (EBP), are shown in Figure 1. It is extracted from the EBSI's technical specification on their website [[https://ecas.ec.europa.eu/](https://ecas.ec.europa.eu/)]([https://ecas.ec.europa.eu/](https://ecas.ec.europa.eu/)) (accessed on 8 April 2022). The two main elements for the management systems of these digital identities are highlighted by [PERSON] [30]:  
_SSI leverages two essential elements for identity management: decentralized registers of information and digital wallets. Decentralized ledgers: The SSI model relies on decentralized registers of information, in which the proofs of ownership of decentralized identifiers and the verifiable credentials are stored within a decentralized ledger.