3. Architecture Patterns & Case Studies

This section complements the structural description of the European Interoperability Reference Architecture (EIRA) by illustrating how its architectural concepts are applied in practice. It introduces a set of common interoperability patterns, domain-specific use cases, and concrete case studies drawn from real deployments.

The objective is twofold: first, to demonstrate how recurring interoperability challenges can be addressed through reusable architectural approaches; and second, to show how EIRA and its extension through eGovERA support the consistent realisation of these approaches across policy domains and levels of government.

By linking abstract Architecture Building Blocks (ABBs) and Enablers to Solution Building Blocks (SBBs) and operational solutions, this section supports the understanding of practitioners in translating architectural guidance into implementable designs while fostering reuse, alignment, and interoperability by design.

3.1. Architecture patterns

Interoperability patterns describe recurrent architectural solutions to common interoperability needs observed across public sector systems. Rather than prescribing specific technologies, these patterns define stable combinations of responsibilities, interactions, and constraints that can be realised through different implementations.

Following, some cases that EIRA and eGovERA cover, these are not the only patterns, but rather, examples:

• Federated Identity and Access Management. This pattern addresses cross-organisational and cross-border authentication and authorisation. In EIRA, it relies on identity, trust, and access control Enablers, including identity management, authentication, authorisation, and trust frameworks. eGovERA documents concrete realisations of this pattern through reusable solutions enabling federated identity, single sign-on, and attribute exchange across administrations.

• Cross-Domain Data Exchange. This pattern supports the controlled exchange of data between heterogeneous systems and organisations (e.g. European Commission institutions and systems, Members States, etc). It builds on Enablers related to interoperability interfaces, messaging, data transformation, and governance. eGovERA solutions realising this pattern include data exchange infrastructures, interoperability platforms, and common service layers facilitating secure and standard-based data sharing.

• Data Spaces and Data Sharing Ecosystems. Data space patterns address multi-stakeholder data sharing scenarios based on common governance, semantic alignment, and technical interoperability. EIRA captures these through Enablers related to data governance, metadata management, semantic assets, and trust services. eGovERA documents operational data space solutions that realise these Enablers in specific policy contexts.

As already mentioned, these are a few examples that the reference architectures are covering, but a wider range is covered within the models. The ultimate value is provide a structured path from architectural intent to deployable solutions while maintaining technology neutrality.

3.2. The Domain Specific Reference Architectures: Health, Customs, and Tax

In addition to the cross-cutting interoperability patterns, eGovERA extending EIRA supports domain-specific solution development, which implies domain-specific legal, organisational, and operational constraints. To address this, a set of sectoral use cases are provided to illustrate how the Reference Architectures are applied in concrete policy domains.

3.2.1. eGovERA Health Reference Architecture [5]

The health use case addresses highly sensitive data exchange scenarios, including patient identification, electronic health records, and cross-border healthcare services. It illustrates the application of EIRA Enablers related to data protection, consent management, semantic interoperability, and trust. This use case shows how interoperability can be achieved while respecting strict legal and ethical requirements, and how common architectural patterns support continuity of care across organisational and national boundaries.

3.2.2. eGovERA Customs Reference Architecture [6]

The customs use case focuses on interoperability between customs authorities, economic operators, and other border management agencies. It demonstrates how EIRA supports complex, multi-actor processes such as goods declaration, risk analysis, and information sharing across jurisdictions.

3.2.3. eGovERA Tax Reference Architecture [7]

The taxation use case focuses on interoperability scenarios such as cross-border information exchange, taxpayer identification, and coordination between tax authorities. It demonstrates how common architectural elements—such as identity management, secure data exchange, and semantic alignment of fiscal data—are combined to support compliance, transparency, and efficiency. The use case highlights how shared Enablers enable interoperability while allowing national administrations to retain autonomy over internal systems.

3.3. Case studies, the Reference Architectures in use

There are different cases where EIRA and eGovERA have been used by public administrations to analyse and design solution (digital public services) interoperable by design and tailored to cover the specific needs and requirements of each of their use cases.

3.3.1. eGovERA© success story on a Data Space and Linked Data in Flanders [8]

DG DIGIT helped the Flemish agency for Home Affairs design a Solution Architecture Template for “Locally Taxed”, a data space reusing local tax decisions from over 3.000 local governments within the Flemish region to power citizen advisory services, producing analysis and a partial solution designs models in ArchiMate. Key success factors were clear milestones, a multidisciplinary team, and alignment with EU goals. The models and methods provide reusable insights for the future Smart City/Data Space work and stakeholder-ready templates.

3.3.2. eGovERA success on a Data Space with the Council of Madrid [9]

DG DIGIT supported Madrid’s Smart Urban Spaces - specifically MercaMadrid - by creating an eGovERA-based SAT and partial solution model to ensure interoperability across IoT-driven services (environment, waste, lighting) via a data space, with outputs in ArchiMate for reuse. Benefits include a scalable template to document smart spaces, guide future tenders, and enable replicability, cybersecurity, and digital-twin/open data integration. Success factors were knowledge dissemination and a model adaptable to other spaces; initial complexity was offset by ensuring interoperable exchange between the city and providers.

3.3.3. eGovERA success on ViDA e invoicing requirements with DG TAXUD [10]

Under Fiscalis FPG/042, DG TAXUD and DG DIGIT used eGovERA’s Tax Reference Architecture to produce SAT models for “B2B intra community transactions e Invoicing reporting,” centralizing requirements to support Member States implementing ViDA e invoicing. The group (nine countries) highlighted clear onboarding, blended sessions, and alignment with EIF as key success factors. While benefits must be proven nationally and local adaptation is pending, the approach promotes standardization, cross border alignment, and reuse; more eGovERA centered use cases are encouraged to address change resistance and demonstrate impact.

3.3.4. First public procurement use case for EIRA and ITB with CACSA [11]

Valencia’s CACSA applied EIRA and the Interoperability Test Bed across a full public procurement for a new “Sede Electrónica,” using EIRA to structure technical specifications and ITB for quality control. This aligned procurement with EIF, expressing capabilities as Architecture Building Blocks to ease evaluation and ensure interoperability from requirements to award and post award activities. The case demonstrates how EIRA+ITB can improve specification clarity, comparability, and assurance, offering a replicable blueprint for other public administrations seeking interoperable, cross border ready digital public services

3.4. References

[5]

eGovernment European Reference Architecture Health Domain. See appendices for domain-specific reference architecture documentation.

[6]

eGovernment European Reference Architecture Customs Domain. See appendices for domain-specific reference architecture documentation.

[7]

eGovernment European Reference Architecture Tax Domain. See appendices for domain-specific reference architecture documentation.

[8]

European Commission, DG DIGIT. Flanders Data Space Case Study: Locally Taxed Initiative. Available in the appendices and case study collection.

[9]

European Commission, DG DIGIT. Madrid Smart Urban Spaces Case Study. Available in the appendices and case study collection.

[10]

European Commission, DG TAXUD and DG DIGIT. ViDA e-Invoicing Reference Architecture Case Study under Fiscalis Framework. Available in the appendices.

[11]

European Commission. CACSA Valencia Public Procurement Case Study: EIRA and Interoperability Test Bed Application. Available in the appendices and best practices documentation.