In January 2023, the ISO adopted as a recognised ISO standard the open protocol OASIS ebXML registry and repository (RegRep) Version 4.0, the technical specification used by the Once-Only Technical System (OOTS) for evidence location and evidence exchange.

The adoption of OASIS ebXML registry and repository (RegRep) as an ISO standard is important, notably because the use of open standards that are independent of any particular vendor implementation is a core principle of the architecture of the Once-Only Technical System.

Evidence location and evidence exchange within the OOTS

When completing an online procedure, citizens will be able to give their explicit request to use the Once-Only Technical System to locate and retrieve evidence from a competent authority in another Member State. The explicit request triggers the retrieval of evidence from competent authorities across many different sectors through the Once-Only Technical System (certificates for education, registrations for vehicles, population registers etc.).

The Once-Only Technical System puts into practice the Once-Only Principle, which states that citizens should not be forced to provide information to authorities if another authority already holds that information in electronic format.

The Once-Only Technical System consists of seven steps. Establishing the location of evidence (step two below) is a key step to determine the provider of the user’s requested evidence. The exchange of evidences is another fundamental component of the Once-Only Technical System, specifically regarding steps three and six below.

1. Authentication (the person using the system identifies themselves)
2. Evidence location (the relevant procedure portal must identify what to ask for (evidence type), and who to ask it from (the evidence provider)
3. Evidence request (a request for evidence is sent to the evidence provider)
4. Redirection (redirected to the provider side)
5. Preview (the person using the system clearly sees the evidence (a marriage certificate, for example) and can consent in an informed manner)
6. Evidence response (the evidence provider sends the relevant evidence to the evidence requester)
7. Submission (the person submits the data in the relevant administrative procedure)

The evidence request is the message created by the evidence requester, containing all the necessary information for requesting an evidence. The evidence response is the answer to an evidence request created by the evidence provider and sent to the evidence requester (either success, error or failure).

The Once-Only Technical System uses version four (v4) of the OASIS Electronic business eXtensible Markup Language (ebXML) Registry and repository (RegRep) for evidence location and for evidence exchange.

The Once-Only Technical System is based on the ‘four-corner’ model used by the eDelivery building block to exchange between the evidence requester and the evidence provider. eDelivery uses the AS4 message exchange protocol to ensure secure and reliable data exchange. As an ISO standard, RegRep joins AS4 as a member of the ISO 15000 group, as 15000-3.

To understand how RegRep is used in the Once-Only Technical System, you can consult the technical design documents on evidence lookup and on evidence exchange.

For more information on the Once-Only Technical System, visit the Once-Only Hub.

The ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies).