Alexandria: The Vocabulary Hub

Alexandria is a Vocabulary Hub: the essential semantic intermediary in modern dataspaces that enables true semantic interoperability and automated conformance verification across participants.

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The Role of a Vocabulary Hub in Modern Dataspaces

In a dataspace, sovereign data exchange between autonomous Connectors requires a shared understanding of data structures, service offerings, and usage policies. While baseline information models define foundational data exchange concepts, domain-specific vocabularies are essential to describe specialized industrial data (mobility, manufacturing, healthcare, energy).

Alexandria serves three foundational functions in the dataspace:

1. Vocabulary Lifecycle & Publishing

• Single Source of Truth: A central repository where domain experts author, document, version, and publish domain ontologies, RDF vocabularies, and dataset profiles.
• Extending Baseline Models: Bridges standard dataspace namespaces with domain-specific Linked Data schemas without requiring advance bilateral agreements.

2. Runtime Semantic Dereferencing

• Dynamic Term Lookups: When a Connector encounters an unfamiliar attribute IRI in a participant's Self-Description or contract offer, it dereferences that IRI against Alexandria.
• Machine-Readable Response: Alexandria immediately responds with the term's RDF definition, class hierarchy, multilingual labels, and semantic relations.
• Namespace Caching: Connectors can query whole namespaces to cache entire vocabularies locally, reducing runtime latency.

3. Remote Conformance Testing

• Automated Semantic Verification: Data providers and connectors can run remote conformance tests against the hub using SHACL (Shapes Constraint Language) validation shapes.
• Payload & Profile Compliance: Verifies that dataset schemas, catalog records, and connector payloads conform to published dataspace specifications before transactions occur.
• Semantic Integrity: Prevents malformed or non-compliant data models from degrading dataspace interoperability.

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Identity & SSI: The Trust Anchor

Before participants can publish vocabularies or execute remote conformance validations, the hub requires robust, cryptographically verifiable trust:

• Decentralized Identifier (DID): Alexandria holds an autonomous DID and serves its resolvable DID Document at /.well-known/did.json.
• Delegated Key Custody: Cryptographic signing keys are held externally via the wallet.Wallet port, supporting Fafnir and Eclipse EDC IdentityHub.
• Node-Terminated Authentication: APIs are protected behind Zitadel using OIDC and PKCE, issuing encrypted HttpOnly session cookies.

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Next Steps