Exploring synergies between the SDG Once-Only Technical System and other key initiatives

Article 19 of the Interoperable Europe Act mandates the identification of synergies with other Union and national initiatives that promote interoperability. In line with this, the INVEST project investigates synergies between key EU digital infrastructures, including the Single Digital Gateway Once-Only Technical System (SDG OOTS), the European Digital Identity Wallet (EUDI Wallet), cross-border European systems, and public data spaces.

INVEST analyzes and maps these synergies to produce policy recommendations that bridge national implementations with EU-level interoperability frameworks. By promoting alignment between the SDG OOTS, EUDI Wallet infrastructures, common data models, and public data spaces, INVEST aims to foster a coherent digital ecosystem enhancing user convenience, administrative efficiency, and trust.

This holistic approach ensures that the once-only principle, digital identity management, and data governance complement each other, ultimately advancing the EU’s vision of a seamless, secure, and interoperable Digital Single Market aligned with the Interoperable Europe Agenda.

The Single Digital Gateway Regulation mandates that citizens and businesses should only have to provide information once when dealing with public authorities across the EU. The OOTS is the technical enabler of this vision - built on strong interoperability principles and secure infrastructure, it automates cross-border data exchange for procedures such as applying for university admission, business registration and recognition of academic qualifications.

To avoid duplication and maximize efficiency, OOTS is designed to connect with existing, proven European systems. Examples include:

• RESPER and EUCARIS for vehicle and driving licence data
• EMREX for educational records
• EESSI for social security exchanges
• ECRIS for judicial cooperation
• eCertis for public procurement documentation

These integrations are helping to create a pan-European intergovernmental data space, aligned with the Common European Data Space for public administrations, where national authorities act as trusted, authoritative data providers.

The effectiveness of OOTS is amplified through synergies with several major EU initiatives. These synergies manifest in semantic alignment, organizational collaboration, and technical interoperability:

SDG-OOTS & Public Administration Data Spaces

• By applying OOTS-compatible structured data models, public administrations ensure meaningful, interoperable exchanges across systems and borders.
• Collaboration between SDG and data space expert groups leads to harmonized governance and shared standards.
• Common Services provided by the European Commission for OOTS are foundational to a shared infrastructure for digital innovation.

SDG-OOTS & ISA² Core Vocabularies

• Core Vocabularies (e.g., Person, Business, Location) from ISA² align with the OOTS data model to standardize information structure and semantics.
• Coordinated work between ISA² and OOTS stakeholders streamlines data modeling and governance strategies.

SDG-OOTS & Existing European Document Exchange Systems

• Leveraging data models from established systems like EUCARIS and EMREX accelerates evidence exchange model development.
• Aligning technical architectures ensures secure, interoperable, and efficient cross-border data flows.

Enabling Trust and Security: eIDAS and the EU Digital Identity Wallet

OOTS relies heavily on trusted identity verification, which is where the eIDAS Regulation and the emerging EU Digital Identity Wallet (EUDI) come into play.

• eIDAS provides the legal and technical framework for mutual recognition of electronic identification (eID) across borders, ensuring that cross-border users can securely access services.
• The EUDI Wallet allows users to control their digital credentials and share verified information seamlessly and securely.

Benefits of integration:

• eIDAS networks and future wallet-based IDs integrate smoothly into OOTS workflows.
• Combining automatic document retrieval via OOTS with user-controlled identity credentials from the wallet simplifies and personalizes interactions.
• Co-development avoids redundancy by unifying legal, technical, and governance frameworks.

As these synergies unfold, the SDG-OOTS becomes more than just a technical system - it becomes the backbone of a truly interoperable, citizen-focused digital Europe. By leveraging existing systems, harmonizing data models, aligning regulatory frameworks, and fostering collaborative governance, the EU is not just building better services. It is creating a resilient and trusted digital public sector for the future.