The Once Only Hub.Collaborate to build the future of the Single Market
The EU is making it easier for citizens to study, move, work, retire or do business. The Once-Only Technical System will connect EU public authorities, so they can exchange official documents and data at the citizen’s request. It puts into practice the Once-Only Principle (OOP), which states that citizens should not be forced to provide information to authorities if another authority already holds that information in electronic format.
Who's the HUB for?
SDG coordination group
Actors responsible for building and maintaining the Once-Only Technical System between Member States.
Competent authorities
The authorities who must allow their users to retrieve requested evidence using the Once-Only Technical System.
Interested parties
Everyone who wants to learn more about the Once-Only Technical System.
Architectural design of the Once Only Technical System
The Once-Only Technical System is a technical framework for data sharing. Citizens and businesses will be able to request “evidence” to complete administrative procedures (allowing people to study, work, live and retire in other EU countries). The decentralised architecture connects public authorities, so they can exchange official documents and data at the citizen's request.
The citizen or business is identified and, having actively confirmed that the Once-Only Technical System should be used, is shown a list of the types of document that are possible to be retrieved directly from data sources abroad. The citizen will then select which documents they wish to retrieve from the data sources.
Technical 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 resulting from the common efforts of the Commission and Member States.
Chapter 1
Introduction - High Level Architecture
This chapter introduces the high-level architecture of the OOTS and the key concepts and themes found in the subsequent chapters.
Chapter 2
User Identification, Authentication and Record Matching
This chapter explains how evidence requesters or evidence provider are identified and authenticated when performing a procedure using the OOTS to exchange evidence. This chapter looks at the use and purpose of the eID Building Block and eIDAS attributes in the OOTS to support user identification and authentication.
Chapter 3
Common services
This chapter looks at those Common Services identified by the Member States and European Commission necessary for the proper execution of the evidence exchange process within the OOTS:
- Data Service Directory (DSD)
- Evidence Broker (EB)
- Semantic Repository (SR).
Chapter 4
Evidence Exchange
This chapter describes correlated messages and how the Once-Only Technical System (OOTS) specifications define in detail the structure, content and message exchange parameters.
Chapter 5
Data Models
This chapter has coveres the semantic interoperability issues in designing the single technical system for the SDG and ensuring its interconnection with EU Member States' IT systems and EU-level systems.
Chapter 6
OOTS Guidance & UX Recommendations
This chapter provides a high-level overview of how the Once-Only Technical System (OOTS) of the Single Digital Gateway (SDG) works as well as detailed UX recommendations.
Common services
The common services are necessary for the proper execution of the evidence exchange process.
Evidence Broker (EB)
This service is an authoritative system that maps specific data sets as Evidence types that prove specific requirements. The consults the to find which types of evidence can be requested as evidence for a specific Evidence Subject, taking into account the Subject's location and/or jurisdiction.
Data Service Directory (DSD)
This common service acts as a catalogue of Evidence types that the can provide upon request. It is used in the Evidence Exchange process by the Evidence Requesters to discover the Evidence Providers that can provide the evidence they require.
Semantic Repository (SR)
This common service that act as a data portal for OOTS, storing commonly agreed information models grouped by domain, providing them under multiple representation techniques.
Supporting services
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Testing
The goal of the OOTS Testing services is to assist Member State teams in implementing the Once-Only Technical System (OOTS) as defined in the Implementing Regulation (IR) and Technical Design Documents (TDDs). Information on the available testing services, including the test platform and tools to facilitate testing can be found on the following protected wiki space
Member State teams that would like to get access are invited to contact their National Coordinator or the EC OOTS Support Desk via mail: EC-OOTS-SUPPORT@ec.europa.eu
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Service desk
The service desk helps Contributors get access to the Confluence and answers to any technical issues. Contributors are added to specific user groups which allow them to see the dedicated pages of the sub-groups they are working on.