The Once-Only Hub.Collaborate to build the future of the Single Market.
The Once-Only Technical system connects EU public authorities, so they can exchange official documents and data at the citizen’s request. It 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.
Who is the Once-Only Hub for?
The Hub is primarily for implementers from the EU Member States, building and maintaining the Once-Only Technical System. It is a single environment providing reliable information, services and support.
Anyone can browse the Hub to learn more about the system, programme and the key benefits for EU citizens and businesses.
Architectural design of the Once-Only Technical System
The Once-Only Technical System (OOTS) is a technical framework for data sharing. Citizens and businesses will be able to request official documents (known as “evidence”) to complete administrative procedures allowing people to study, work, live and retire in other EU countries in 7 simple steps. The decentralised architecture connects public authorities, so they can exchange evidence at the citizen's or business' request.
There is a guidance document available that provides a high-level overview and introduction to the way the Once-Only Technical System will work.
The 7 steps of the Once-Only Technical System:
- 1
Authenticate: The user authenticates with an eIDAS notified eID scheme
- 2
Locate evidence: The procedure portal identifies what to ask for (Evidence Type), and who to ask it from (Evidence Provider)
- 3
Evidence request: The request for evidence is sent to the Evidence Provider
- 4
Redirect: The user is redirected to the provider side
- 5
Preview: The user previews their evidence
- 6
Evidence response: The Evidence Provider responds to the evidence request
- 7
Submit: The user completes and submits his/her procedural form
Documentation
The technical and operational specifications of the Once-Only Technical System, laid down in the Commission’s Implementing Regulation ((EU) 2022/1463) setting out the system, are complemented by detailed, non-binding technical design documents jointly prepared by the Commission and Member States.
Chapter 1
Introduction - High Level
Architecture
This chapter introduces the high-level architecture of the Once-Only Technical System and the key concepts and themes found in the subsequent chapters.
Chapter 2
User Identification, Authentication and Record Matching
This chapter explains how those submitting or receiving evidences through the Once-Only Technical System are identified and authenticated.
Chapter 3
Common Services
This chapter looks at the Common Services necessary for the proper execution of the evidence exchange process.
Chapter 4
Evidence Exchange
This chapter introduces evidence exchange in the Once-Only Technical System, which is based on bilateral data exchange between relevant authorities.
Chapter 5
Data Models
This chapter looks at the data models that streamline the exchange of evidences, together with a methodology for defining new data models and code lists.
Chapter 6
OOTS Guidance & UX
Recommendations
This chapter provides an overview of how the Once-Only Technical System works as part of the wider Single Digital Gateway and looks at the first set of UX recommendations.
Common services
The Commission provides Common Services to help the Member States ensure the proper exchange of evidences.
Data Service Directory
The Data Service Directory is a common service that acts as a catalogue of evidence types that can be provided upon request.
Evidence Broker
The Evidence Broker is an authoritative system that maps specific data sets as evidence types that prove specific requirements.
Semantic Repository
The Semantic Repository is a common service that acts as a data portal for the technical system.
Supporting services
Testing service
The OOTS Testing service assists national teams in implementing the Once-Only Technical System. Information on available texting services, including the test platform and other tools to facilitate testing are available on a restricted wiki space.
If required, please request access via the Service Desk.
Contact the service desk on EC-OOTS-SUPPORT@ec.europa.eu
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Single Digital Gateway Coordination Group
The mission of this group is to coordinate the implementation work around the setup of the Once-Only Technical System. The members of this group are the Member States (and other public entities).
Single Digital Gateway Coordination sub-groups
Six sub-groups have been set-up to examine specific topics related to the Once-Only Technical System and are expected to report to the Single Digital Gateway Coordination Group. They enable the participation of all Member States in the discussion and ensure the work done by Member State experts is monitored.
Service desk
This Service Desk helps users improve the performance, continuity and reliability of their Once-Only Technical system implementations.