Skip to main content


To support the exchange of evidences between Data Services and Online Procedure Portals, the Once-Only Technical System uses Once-Only supporting services. These are referred to as the Common Services. The Common Services do not process data about citizens or businesses. Instead they contain and serve operational data parameters that support the operation of the Once-Only technical system. There are three Common Services:

Evidence Broker (EB)
Data Service Directory (DSD)
Semantic Repository (SR)

The Common Services of the OOTS provide machine-to-machine REST APIs for querying. This section specifies the normative common part of these APIs using the OASIS Regrep 4.0 standard. Services implementing these interfaces MUST adhere to the following interface specifications. For look-ups, all common services shall implement the REST APIs introduced in this section. Currently, this section is limited to the Evidence Broker and Data Service Directory. More details are provided in the technical design documents available from the chapter 3 of the OOTS hub site.

The Once-Only Technical System follows a hybrid deployment model. The Commission will provide a production implementation of the Common Services that Member States can use as a service. Other Member States may implement these services themselves. Each of these services will provide a life-cycle management interface to maintain the data it serves as this data is subject to change over time. That interface uses eDelivery instead of REST and is not covered here.

Access the Common Services

Evidence Broker icon

Evidence Broker

The Evidence Broker is an authoritative system that maps specific data sets as evidence types that prove specific requirements.
Go to Evidence Broker
Data Service Directory icon

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.
Go to Data Service Directory
Semantic Repository icon

Semantic Repository

The Semantic Repository is a common service that acts as a data portal for the technical system.
Go to Semantic Repository