Schema-Governed federation for long-lived digital product passports

Digital Product Passports (DPPs) are becoming regulated, long-lived information artefacts in European product markets. They must remain interpretable and verifiable while the schemas that define them, the platforms that host them, and the DPPs they reference evolve independently. Existing ecosystem-level and ontology-based proposals specify identifiers, discovery mechanisms, trust infrastructure, and content vocabularies, but leave the platform-internal data architecture for versioning, schema binding, and dependency governance largely unspecified. This paper addresses that gap with a formal data architecture for schema-governed DPP federation. The architecture separates persistent logical DPP identity from immutable, schema-bound revisions, distinguishes version-pinned hard references from floating soft references, and uses a resolver-governed schema dependency graph to prevent cyclic hard dependencies before revisions are issued. Seven invariants capture revision uniqueness, revision history, schema explicitness, revision integrity, schema conformance, schema-graph acyclicity, and hard-reference resolvability. We specify the operations that create revisions, publish schemas, resolve references, register issuers, migrate issuer routing, and cache schemas, and show that these operations preserve the invariants under their stated preconditions. The evaluation combines formal coverage analysis, analytical cost analysis, and scenario-based feasibility checks on heterogeneous platform implementation stacks. The results show how long-term DPP interpretability can be treated as a governed federation property rather than as a storage responsibility of individual platforms.