The Once Only Hub.Building the European data-space.
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, 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?
Implementers from EU Member States, building and maintaining the Once-Only Technical System. A single environment providing them with information and access to services.
Anyone can browse the Hub to learn more about the system, program and the benefits for them.
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. The decentralised architecture connects public authorities, so they can exchange evidences (official documents) at the citizen's request.
The citizen or business is identified and, having actively confirmed that they wish to use the Once-Only Technical System, 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.
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 (provided by the Commission) 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 the following Common Services to allow for the proper exchange of evidences.
Data Service Directory (DSD)
The Data Service Directory is a common service that acts as a catalogue of evidence types that can be provided upon request.
Evidence Broker (EB)
The Evidence Broker is an authoritative system that maps specific data sets as evidence types that prove specific requirements.
Semantic Repository (SR)
The Semantic Repository is a common service that acts as a data portal for the technical system.
Supporting services
Testing service
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.
Access a test platform and tools through our secure testing service
Request access via your National Coordinator or the Support Desk directly via EC-OOTS-SUPPORT@ec.europa.eu
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Service desk
This Service Desk provides helps users improve the performance, continuity and reliability of their Once-Only Technical system implementations.