Federation Services

The Federation Services are necessary to enable a Federation of infrastructure and data, provided with open source reference implementation. This will open up technology where applicable, while existing Certifications and standards for Accreditation will be recognized.

Details about the operationalization of the Federation Service will be outlined in the upcoming Federation Services documents. Details about the role of Federation Services for Ecosystems are elaborated in section [Gaia-X Ecosystems] , with an overview shown in the figure below.

  • The [Federated Catalogue] constitutes the central repository for Gaia-X Self-Descriptions to enable the discovery and selection of Providers and their Service Offerings. The Self-Description as expression of properties and Claims of Participants and Assets represents a key element for transparency and trust in Gaia-X.

  • [Identity and Trust] covers authentication and authorization, credential management, decentral Identity management as well as the verification of analogue credentials.

  • [Data Sovereignty Services] enable the sovereign data exchange of Participants by providing a Data Agreement Service and a Data Logging Service to enable the enforcement of Policies. Further, usage constraints for data exchange can be expressed by Provider Policies as part of the Self-Description.

  • [Compliance] includes mechanisms to ensure a Participant’s adherence to the Policy Rules in areas such as security, privacy transparency and interoperability during onboarding and service delivery.

  • [Gaia-X Portals and API] will support onboarding and Accreditation of Participants, demonstrate service discovery, orchestration and provisioning of sample services.

Gaia-X Federation Services and Portal as covered in the Architecture Document

Federated Catalogue

Self-Descriptions intended for public usage can be published in a Catalogue where they can be found by potential Consumers. The Providers decide in a self-sovereign manner which information they want to make public in a Catalogue and which information they only want to share privately. The goal of Catalogues is to enable Consumers to find best-matching offerings and to monitor for relevant changes of the offerings.

A Catalogue contains two types of storage: The Self-Description Storage for the published Self-Description files and the Self-Description Graph. By following references between Self-Descriptions in the graph, advanced queries across individual Self-Descriptions become possible.

The system of Federated Catalogues comprises a top-level Catalogue operated by the Gaia-X, European Association for Data and Cloud, AISBL as well as Ecosystem-specific Catalogues (e.g., for the healthcare domain) and even company-internal Catalogues with private Self-Descriptions to be used only internally. Self-Descriptions in a Catalogue are either loaded directly into a Catalogue or exchanged from another Catalogue by an inter-Catalogue synchronization interface.

Since Self-Descriptions are protected by cryptographic signatures, they are immutable and cannot be changed once published. The lifecycle state of a Self-Description is described in additional metadata. There are four possible states for the Self-Description lifecycle. The default state is “active”. The other states are terminal, i.e., no further state transitions follow upon them:

  • Active

  • End-of-Life (after a timeout date, e.g., the expiry of a cryptographic signature)

  • Deprecated (by a newer Self-Description)

  • Revoked (by the original issuer or a trusted party, e.g., because it contained wrong or fraudulent information)

The Catalogues provide access to the raw Self-Descriptions that are currently loaded including the lifecycle metadata. This allows Consumers to verify the Self-Descriptions and the cryptographic proofs contained in them in a self-sovereign manner.

The Self-Description Graph contains the information imported from the Self-Descriptions that are known to a Catalogue and in an “active” lifecycle state. The Self-Description Graph allows for complex queries across Self-Descriptions.

To present search results objectively and without discrimination, compliant Catalogues use a graph query language with no internal ranking of results: Besides the user-defined query statements with explicit filter- and sort-criteria, results are ordered randomly. The random seed for the search results can be set on a per-session basis so that the query results are repeatable within a session with a Catalogue.

In a private Catalogue, the authentication information can be used to allow a user to upload new Self-Descriptions and/or change the lifecycle state of existing ones. In a public Catalogue, the cryptographic signatures of the Self-Descriptions are checked if its issuer is the owner of its subject. If that is the case, the Self-Description is accepted by the Catalogue. Hence, Self-Descriptions can be communicated to the Catalogue by third parties, as the trust verification is independent from the distribution mechanism. Self-Descriptions can be marked by the issuer as “non-public” to prevent them from being copied public Catalogue by a third-party that received the Self-Description JSON-LD file over a private channel.

A Visitor is an anonymous user accessing a Catalogue without a known account for session. Every Non-Visitor user (see Principal in section 3.2) interacts with a Catalogue REST API in the context of a session. Another option to interact with a Catalogue is to use a GUI frontend (e.g. a Gaia-X Portal or a custom GUI implementation) that uses a Catalogue REST API in the background. The interaction between a Catalogue and its GUI frontend is based on an authenticated session for the individual user of the GUI frontend.


Gaia-X Self-Descriptions express characteristics of Assets, Resources, Service Offerings and Participants are tied to their respective Identifier. Providers are responsible for the creation of their Asset’s or Resource’s Self-Description. In addition to self-declared Claims made by Participants about themselves or about the Service Offering provided by them, a Self-Description may comprise Credentials issued and signed by trusted parties. Such Credentials include Claims about the Provider or Asset/Resource, which have been asserted by the issuer.

Self-Descriptions in combination with trustworthy verification mechanisms empower Participants in their decision-making process. Specifically, Self-Descriptions can be used for:

  • Discovery and composition of Service Offerings in a Catalogue

  • Tool-assisted evaluation, selection, integration and orchestration of Service Instances comprising Assets and Resources

  • Enforcement, continuous validation and trust monitoring together with Usage Policies

  • Negotiation of contractual terms concerning Assets and Resources of a Service Offering and Participants

Gaia-X Self-Descriptions are characterized by the following properties:

  • Machine-readable and machine-interpretable

  • Technology-agnostic

  • Adhering to a generalized schema with an expressive semantics and validation rules

  • Interoperable, following standards in terms of format, structure, and included expressions (semantics)

  • Flexible, extensible and future-proof in that new properties can be added

  • Navigable and can be referenced from anywhere in a unique, decentralised fashion

  • Accompanied by statements of proof (e.g., certificates and signatures), making them trustworthy by providing cryptographically secure verifiable information

A possible exchange format for Self-Descriptions can be the JSON-LD format. JSON-LD uses JSON encoding to represent subject-predicate-object triples according to the W3C Resource Description Framework (RDF).

The Self-Description of one entity may refer to another entity by its Identifier. These relations form a graph with typed edges, which is called the Self-Description Graph. The Catalogues implement a query algorithm on top of the Self-Description Graph. Furthermore, Certification aspects and Usage Policies can be expressed and checked based on the Self-Description Graph that cannot be gained from individual Self-Descriptions. For example, a Consumer could use Catalogue Services to require that a Service Instance cannot depend on other Service Instances that are deployed on Nodes outside a Consumer-specified list of acceptable countries.

A Self-Description contains the Identifier of the Asset, Resource or Participant, metadata and one or more Credentials as shown in the figure below. A Credential contains one or more Claims, comprised of subjects, properties and values. The metadata of each Credential includes issuing timestamps, expiry dates, issuer references and so forth. Each Credential can have a cryptographic signature, wherein trusted parties confirm the contained Claims. Claims may follow the same subject–property–object structure of the data model. The W3C Verifiable Credentials Data Model1 is a possible technical standard to express Credentials and Claims on top of JSON-LD2.

graph LR subgraph Self-Description metadata1[Metadata] vc1[Verifiable Credential - 1..*] proof1[Proof Info - 1..*] end subgraph Verifiable Credential metadata2[Metadata] claim[Claim - 1..*] proof2[Proof Info - 1..*] end vc1 -- 1 .. * --> claim %% classDef attribute fill:#f9f,stroke:#333,stroke-width:4px,rx:50%,ry:50%; %% classDef attribute stroke-width:2px,rx:50%,ry:50%; class iso,date attribute;

Self-Description assembly model

The generic data model for Claims is powerful and can be used to express a large variety of statements. Individual Claims can be merged together to express a graph of information about an Asset/Resource (subject). For example, a Node complying with ISO 27001 is shown in the figure below.

graph TB subgraph Credential Graph cred123[Credential 123] -- credentialSubject --> node[Node] cred123 -- issuer --> duv[DUV] node -- hasCertificate --> iso(ISO 27001) end subgraph Proof Graph sig456[Signature 456] -- creator --> jane[Jane Doe] sig456 -- created --> date(2021-03-01 14:01:46) end duv -- proof --> sig456 %% classDef attribute fill:#f9f,stroke:#333,stroke-width:4px,rx:50%,ry:50%; %% classDef attribute stroke-width:2px,rx:50%,ry:50%; class iso,date attribute;

Linked Claim statements as a graph representation

To foster interoperability, Self-Description schemas with optional and mandatory properties and relations are defined. A Self-Description has to state which schemas are used in its metadata. Only properties and relations defined in these schemas must be used. A Self-Description schema corresponds to a class in RDF. The Self-Description schemas form an extensible class hierarchy with inheritance of properties and relations.

The Gaia-X Federation Services specification describes how core Self-Description schemas based on the conceptual model are created and maintained. Individual Gaia-X Ecosystems can extend the schema hierarchy for their application domain.3 Such extensions must make an explicit reference to the organization that is responsible for the development and maintenance of the extension.

Schematic inheritance relations and properties for the top-level Self-Description

The Self-Description Schemas can follow the Linked Data best practices4 making the W3C Semantic Web family5 a possible standard to be built upon to enable broad adoption and tooling.

Gaia-X aims at building upon existing schemas, preferably such that have been standardized or at least widely adopted6 to get a common understanding of the meaning and purpose of any property and Claim statement. Examples of attribute categories per Self-Description in Gaia-X are discussed in the Appendix [A1].

Identity and Trust

Identities, which are used to gain access to the Ecosystem, rely on unique Identifiers and a list of attributes. Gaia-X uses existing identities and does not maintain them directly. Uniqueness is ensured by a specific Identifier format relying on properties of existing protocols. Trust – confidence in the Identity and capabilities of a Participant, Asset or Resource – is established by cryptographically verifying Identities using the Federated Trust Model of Gaia-X, which is a component that guarantees Identity proofing of the involved Participants to make sure that Gaia-X Participants are who they claim to be. In the context of Identity and Trust, the natural person or a digital representation, which acts on behalf of a Participant is referred to as Principal. As Participants need to trust other Participants and Service Offerings provided, it is important that the Gaia-X Federated Trust Model provides transparency for everyone. Therefore, proper lifecycle management is required, covering Identity onboarding, maintaining, and offboarding. The table below shows the Participant Lifecycle Process.

Lifecycle Activity Description
Onboarding The governing body of a Gaia-X Ecosystem validates and signs the Self-Description provided by a Visitor (the future Participant/Principal).
Maintaining Trust related changes to the Self-Descriptions are recorded in a new version and validated and signed by the governing body of a Gaia-X Ecosystem. This includes both information controlled by the Participant/Principal.
Offboarding The offboarding process of a Participant is time-constrained and involves all dependent Participants/Principals.

Participant Lifecycle Process

An Identity is composed of a unique Identifier and an attribute or set of attributes that uniquely describe an entity (Participant/Asset) within a given context. Attributes will be derived from existing identities as shown in the IAM Framework7.

A secure Identifier for an Identity will be assigned by the issuer in a cryptographically secure manner. In addition, the process of identifying the holder of an Identity is transparent. Furthermore, it is traceable since when the Identifier exists in this form, whether it is regularly checked and according to which policy this is done. It must also be possible to revoke issued Identity attributes8.

Trust Framework

Gaia-X defines a trust framework on established standards and EU regulation. The Trust Framework solution supports the privacy and self-sovereign requirements and gains the chain of trust without the need of a global and traceable unique ID across the Ecosystem.

Trust in Gaia-X is established by technical elements, such as technical components and processes as well as by a fair and transparent governing body.

The Gaia-X AISBL is the main trust anchor. Participants trusting AISBL is a prerequisite for a functioning Ecosystem. In this sense, Gaia-X can act as a Federator (according to section [Gaia-X Conceptual Model]). Then, Gaia-X maintains a list of organizations it trusts to carry out tasks like onboarding, Certifications, and so forth. Participants are free to agree on additional trust providing organizations, for example in certain domains. The EU List of eIDAS Trusted Lists9 can also be used as a source for trust service providers and Conformity Assessments Bodies.

Self-Descriptions (see section [Federated Catalogue]) play another crucial part in establishing Trust within Gaia-X. In addition to non-trust-related information, which can be updated by the Participant, they contain trust-related information such as the organization DID and/or the organization IDM OpenID Connect issuer (which connects to the organization’s Identity System). The trust-related part is vetted according to Gaia-X Policy and electronically signed by a trusted organization. Possible later changes regarding the trust related information have to be approved. Gaia-X in turn maintains a Self-Description, which lists its policies and accepted trust providers as mentioned before.

Service Offerings may have different levels of Trust. During service composition, it is determined by the lowest trust state of the Service Offering it relies on. The trust state of a Service Offering will not affect the trust state of a Participant. On the other hand, a Policy violation of a Participant can result in losing the trust state of its service.

Hybrid Identity and Access Management

The Gaia-X IAM Framework supports two different approaches, the federated Identity approach and the decentralized Identity approach.

In the federated Identity approach, a Principal access a standardized query API, which forwards the login request to the Gaia-X Internal Access Management component (Gaia-X AM). The Gaia-X AM requests authentication from the preselected Provider Identity System. The Principal will provide the Credentials to the Identity System. The Identity System validates the inputs and provides attributes to Gaia-X AM, which grants / denies access to Gaia-X. Based on the assigned Principal roles, specific permissions are granted or not.

In the decentralized Identity approach, authentication and authorization in Self Sovereign Identity (SSI) is based on decentralized identifiers (DID)10. Public key infrastructure is used to verify controllership of a certain DID and Verifiable Credential11 that in turn contains any kind of third party issued attributes. Those Verified Credentials can be used to make decisions to grant access to certain Resources (authorization). Depending on the existing system landscape, it may be necessary to set up a “trusted transformation” point to translate between new SSIs and existing Identity Systems. This outsources the issuing and verification of Verifiable Credentials to another component, controlled by an existing Identity System.

Gaia-X might need to comply with additional requirements on the type and usage of credential manager applications, e.g. mandatory minimum-security requirements such as Multi Factor Authentication. Server-to-Server Communication plays a crucial role in Gaia-X and the integration of self-sovereignty will be worked out in more detail.

Federated Trust Model

For achieving Trust between identities, the Federated Trust Model is built around the definition of standardized processes and practices, incorporating general accepted policies as well as domain specific policies derived out of private, industrial, governmental and educational sectors.

Detailed Level Design of the Gaia-X Federated Trust Model

The Federated Trust Model achieves Trust between Consumers and Providers. This is realized with the components shown in Figure 8. While the Federated Trust Component and the Federated Catalogue have been defined before, the Federated Trust Model further involves the Gaia-X AM, which is an internal Gaia-X access management component responsible for authorizing Principals’ interactions within the Gaia-X Portals and the Provider Access Management (Provider AM), which the Provider will use to grant access for the Consumer to Service Instances.

Within the federated approach, Identities are built up of verifiable Claims and shared on a need to know basis. For an operational example of the Federated Trust Model, see [A2].

Access Control

The Access Management covers the internal Gaia-X AM and Provider AM. The Provider AM in Gaia-X validates the Principal on the Consumer side using the Federated Trust Component. End-Users are handled using existing technology at the Consumer. For the Gaia-X AM, roles will be needed for Gaia-X Principals which can be used for the access control. Examples for such roles could be Gaia-X Administrator, Participant Administrator, Principal. Roles will be maintained by the Gaia-X AISBL. Clear policies will be in place concerning processes and responsibilities12

Gaia-X itself enables fine-grained access control-based attribute evaluation. Attributes will be derived from metadata, Self-Descriptions and runtime context (e.g. user Identity and associated properties).

Gaia-X will not implement central access control mechanisms for Assets or Resources. The responsibility stays with the Provider. However, Gaia-X will provide a standardized query API which enables the Provider and Consumer to query and verify the Identity and Self-Description of the respective other party. 

Data Sovereignty Services

Data Sovereignty Services provide Participants the capability to be entirely self-determined regarding the exchange and sharing of their data. They can also decide to act without having the Data Sovereignty Service involved, if they wish to do so.

Informational self-determination for all Participants comprises two aspects within the Data Ecosystem: Transparency of data usages and control of data usages. Enabling Data Sovereignty when exchanging, sharing and using data relies on fundamental functions and capabilities that are provided by Federation Services in conjunction with other mechanisms, concepts, and standards. The Data Sovereignty Services build on existing concepts of usage control that extends traditional access control. Thus, usage control is concerned with requirements that pertain to future data usages (i.e., obligations), rather than data access (provisions).

Capabilities for Data Sovereignty Services

The foundation for Data Sovereignty is a trust-management mechanism to enable a reliable foundation for peer-to-peer data exchange and usage, but also to enable data value chains with multiple Providers and Consumers being involved. All functions and capabilities can be extended and configured based on domain-specific or use case-specific requirements in order to form reusable schemes.

The following are essential capabilities for Data Sovereignty in the Gaia-X Data Ecosystems:

Capability Description
Expression of Policies in a machine-readable form To enable transparency and control of data usages, it is important to have a common policy specification language to express data usage restrictions in a formal and technology-independent manner that is agreed and understood within all Gaia-X Participants. Therefore, they have to be formalized and expressed in a common standard, e.g. ODRL13.
Inclusion of Policies in Self-Description Informational self-determination and transparency require metadata to describe Data Assets including, Provider, Consumer, and Usage Policies as provided by Self-Descriptions and the Federated Catalogues.
Interpretation of Usage Policies For a Policy to be agreed upon, it must be understood by all Participants in a way that enables negotiation and possible technical and organizational enforcement of Policies.
Enforcement Monitoring of data usages is a detective enforcement of data usages with subsequent (compensating) actions. In contrast, preventive enforcement14 ensures the policy Compliance with technical means (e.g., cancel or modify data flow).

Capabilities for Gaia-X Data Sovereignty Services

Functions of Data Sovereignty Services

Information services provide more detailed information about the general context of the data usage transaction. All that information on the data exchange and data usage must be traceable, therefore agreed monitoring and logging capabilities are required for all data usages and transactions. Self-determination also means that Providers can choose to apply no Usage Policies at all.

The Data Sovereignty Services in Gaia-X implement different functions for different phases of the data exchange. Therefore, three phases of the data exchange have to be differentiated:

  • before transaction
  • during transaction
  • after transaction

Before the data exchange transaction, the Data Agreement Service is triggered and both parties negotiate a data exchange agreement. This includes Usage Policies and the required measures to implement those. During the transaction, a Data Logging Service receives logging-messages that are useful to trace the transaction. This includes data provided, data received, policy enforced, and policy-violating messages. During and after the transaction the information stored can be queried by the transaction partners and a third eligible party, if required. The figure below shows the role of mentioned services to enable sovereign data exchange.

Data Sovereignty Services Big Picture

The Data Agreement Service enables data transactions in a secure, trusted, and auditable way. It offers interfaces for the negotiation detailing the agreed terms for planned data exchange. The service is not meant to handle the transaction of data (that is described in the negotiated data contracts).

The Data Logging Service provides evidence that data has been (a) submitted, (b) received and (c) that rules and obligations (Usage Policies) were enforced or violated. This supports the clearing of operational issues but also fraudulent transactions.

The Provider can track if, how, what data was provided, with the Consumer being notified about this. The Consumer can track if data was received or not, and, additionally, track and provide evidence on the enforcement or violation of Usage Policies.


Gaia-X defines a Compliance framework that manifests e.g. in the form of a code of conduct, third party Certifications / attestations, or acceptance of terms and conditions. It is detailed in the Policy and Rules document. Requirements from the field of security (e.g. data encryption, protection, or interoperability) form the basis for this Compliance framework. The main objective of the Federation Service Compliance is to provide Gaia-X users with transparency on the Compliance of each Service Offering.

This Federation Service consists of two components: First, the Onboarding and Accreditation Workflow (OAW) that ensures that all Participants, Assets, Resources and Service Offerings undergo a validation process before being added to a Catalogue. Second, the Continuous Automated Monitoring (CAM) that enables monitoring of the Compliance based on Self-Descriptions. This is achieved by automatically interacting with the service-under-test, using standardised protocols and interfaces to retrieve technical evidence. One goal of the OAW is to document the validation process and the generation of an audit trail to guarantee adherence to generally accepted practices in Conformity Assessment. Besides the general onboarding workflow, a special focus is set on :

  • Monitoring of the Compliance relevant basis
  • Update of the Service Offering that imply re-assurance of Compliance
  • Suspension of Service Offerings
  • Revocation of Service Offerings

Gaia-X Portals and API

The Gaia-X Portals support Participants to interact with central Federation Service functions via a user interface, which provides mechanisms to interact with core capabilities using API calls. The goal is a consistent user experience for all tasks that can be performed with a specific focus on security and Compliance. The Portals provide information on Assets, Resources and Service Offerings and interaction mechanisms for tasks related to their maintenance. The functions of the Portals are further described below.

A Portal supports the registration of organizations as new Participants. This process provides the steps to identify and authorize becoming a Participant. Additionally, organizations are assisted singing up as members of AISBL. Participants are be supported managing Self-Descriptions and organizing Credentials. This includes Self-Description editing and administration. A Portal further offers search and filtering of Service Offerings and Participants, based on Federated Catalogues. Additionally, solution packaging refers to a composition mechanism for the selection and combination of Service Offerings into solution packages to address specific use cases possible with a Portal. To orchestrate the various APIs, an API framework to create a consistent user and developer experience for API access and lifecycle is introduced. An API gateway will ensure security to all integrated services. An API portal will provide a single point of information about available API services and version management. 

  1. W3C. Verifiable Credentials Data Model 1.0: Expressing verifiable information on the Web [W3C Recommendation 19 November 2019]. https://www.w3.org/TR/vc-data-model/ 

  2. W3C. JSON-LD 1.1: A JSON-based Serialization for Linked Data [W3C Recommendation 16 July 2020]. https://www.w3.org/TR/json-ld11/ 

  3. This is in analogy to, e.g., how DCAT-AP specifies the application of DCAT for data portals in Europe; European Commission Semantic Interoperability Community. DCAT Application Profile for data portals in Europe. https://joinup.ec.europa.eu/collection/semantic-interoperability-community-semic/solution/dcat-application-profile-data-portals-europe 

  4. Berners-Lee, T. (2009). Linked Data. W3C. https://www.w3.org/DesignIssues/LinkedData 

  5. W3C. (2015). Semantic Web. https://www.w3.org/standards/semanticweb/ 

  6. Examples include the W3C Organization Ontology (https://www.w3.org/TR/vocab-org/), the community-maintained schema.org vocabulary (https://schema.org/), the W3C Data Catalog Vocabulary DCAT (https://www.w3.org/TR/vocab-dcat-2/), the W3C Open Digital Rights Language (https://www.w3.org/TR/odrl-model/), and the International Data Spaces Information Model (https://w3id.org/idsa/core

  7. For a comprehensive view of the current discussion in the broader Gaia-X community, extra documents from the open working packages can be found on the Gaia-X community platform at https://gaia.coyocloud.com/web/public-link/e01b9066-3823-42a7-b10b-9596871059ef/download

  8. For more on Secure Identities, see Plattform Industrie 4.0: Working Group on the Security of Networked Systems. (2016). Technical Overview: Secure Identities. https://www.plattform-i40.de/PI40/Redaktion/EN/Downloads/Publikation/secure-identities.pdf

  9. European Commission. Trusted List Browser: Tool to browse the national eIDAS Trusted Lists and the EU List of eIDAS Trusted Lists (LOTL). https://webgate.ec.europa.eu/tl-browser/#/ 

  10. W3C. (2021). Decentralized Identifiers (DIDs) v1.0. https://www.w3.org/TR/did-core/ 

  11. W3C. Verifiable Credentials Data Model 1.0: Expressing verifiable information on the Web [W3C Recommendation 19 November 2019]. https://www.w3.org/TR/vc-data-model/ 

  12. For details, see chapter 2.1 in Gaia-X IAM Community Working Group. For a comprehensive view of the current discussion in the broader Gaia-X community, extra documents from the open working packages can be found on the Gaia-X community platform at https://gaia.coyocloud.com/web/public-link/e01b9066-3823-42a7-b10b-9596871059ef/download

  13. W3C. ODRL Information Model 2.2 [W3C Recommendation 15 February 2018]. https://www.w3.org/TR/odrl-model/ 

  14. Currently not in scope of Gaia-X Federation Services