## 4 Proposed Model: Use Cases  
Let us describe three explicative use cases.  
First use case: The home's owner, who is the so-called holder in the SSI paradigm, presents the house's energy certificate to a potential buyer: the verifier. The engineer who issued the certificate (hence, the issuer) has to store on-chain both the cryptographic proofs and the status of the credential; in this way, the energy certificate becomes a verifiable credential. It also becomes a verifiable presentation because the holder presents it to the buyer without changing it. Only the issuer of a credential (hence, only authorized bodies: in this case, the engineer) can revoke a credential following an inspection of the house in the event that the energy status no longer coincides with what was previously assigned to it. Thanks to this mechanism, the revocation does not delete the presentation delivered by the holder to the potential buyer, but a future verification of the credential by a verifier returns the non-validity of the certificate. Note that in this use case, the verifier is an external stakeholder. He cannot access the CDE and can only verify the presentation without resorting to third parties thanks to the verifiable credentials and to the public registry in which the proofs are stored.  
Second use case: During construction, the home's owner wants to check the work in progress. In particular, he/she wants to verify the conformity of the electrical system. Being the owner of the house, he/she will be able to access the digital wallet of his house and verify all the credentials that have been registered by the authorized stakeholders. In particular, he/she will check the credentials regarding the electrical system, which were uploaded by the installer, who has a specific ID. Without resorting to third parties, he/she can verify the validity of all credentials and can thus check the work that has been done.  
Third use case: This use case involves the person responsible for managing the work, e.g, a manager or a public official. The manager works on behalf of the client and must prepare all the documents to be presented to the municipality to obtain, for example, the certificate of habitability. By operating on behalf of the customer, who is, for example, the owner of the house under construction, he/she will have access to the digital wallet of the house and will be able to select from that wallet all the data he/she needs to request the certificate. He/she will build a presentation and present it to the public official, who, without resorting to third parties, will be able to verify that all the information presented is valid, and only in that case will the official proceed to issue the requested certificate, which, in turn, becomes a verifiable credential.  
Note that the identities of the stakeholders who are authorized to issue certified content can be declared using trusted lists published in on-chain registries. Further note that energy certificates, as with every certificate and document that aims to be a verifiable credential, should be issued following a precise credentialing scheme in such a way that their content is understood by all (holder, issuer and verifiers). So proposing schemes for the main certificates and documents related to a building is crucial. Just by standardizing and by the creation of governance models that establish, for example, trusted lists, terminologies and rules, SSI systems could be realized in the near future, thus allowing the integration of current systems with SSI applications such as the proposed dApp.