Schema Governance Through Versioned Policies: Cross-Version Structural Interoperability

Mechanism

The mechanism is constructed around a versioned policy registry, a per-object policy reference, and a compatibility relation. The policy registry stores immutable policy definitions, each identified by a content-addressed digest and tagged with a monotonic version number. A policy definition specifies the canonical fields, type constraints, validation predicates, and semantic obligations that govern objects authored under that version. Policy definitions are append-only: once published, a policy version is never mutated. New versions are issued as new entries, and the prior versions remain consultable indefinitely.

Each object carries a policy reference identifying the version under which it was authored. The reference is part of the object's structural identity and is included in the object's digest, so an object cannot be silently rebound to a different policy version without changing its identity. When an object is validated, the validator resolves its policy reference, retrieves the corresponding policy definition from the registry, and evaluates the object's fields and constraints against that definition. Validation against the wrong version is not merely incorrect; it produces a different validation digest and is detectable as a structural inconsistency.

The compatibility relation defines how objects authored under different versions interact. For each ordered pair of versions, the relation specifies whether objects of the source version are admissible as inputs to operations defined in the target version, and if so, what canonical projection or migration is applied. The relation is itself versioned, deterministic, and append-only: compatibility entries are added as new versions are issued and are never silently revised. This permits cross-version interaction to be reasoned about formally and audited reproducibly across the population.

Backward-compatible upgrades are expressed as compatibility entries that map prior-version objects into the new version's input space without loss. Breaking changes are expressed as the absence of such an entry, or as an entry that requires explicit migration. Deprecation is recorded as a tombstone in the registry that retains the deprecated version's definition but marks it as ineligible for new authorship while preserving its validity for existing objects. This preserves the historical record and supports forensic analysis long after the deprecated version is retired from active use.

Operating Parameters

Version identifiers are monotonic integers paired with content-addressed digests. The integer ordering supports human-readable sequencing and admits efficient range queries; the digest provides cryptographic binding and prevents version aliasing. Operators select a publication cadence for new versions, balancing the cost of registry growth against the granularity of policy change tracking. Typical deployments publish on the order of tens to hundreds of versions per policy family per year, with retention horizons measured in years to decades depending on the regulatory or operational context.

The compatibility relation is parameterized by the projection language used to express migrations. The disclosed embodiment uses a restricted total-function language that admits only field renaming, field projection, default-value insertion, and bounded structural rewriting. General-purpose computation, network access, and unbounded recursion are excluded. This restriction ensures that compatibility procedures terminate, are deterministic, and produce reproducible results across the participant population without requiring synchronized runtime environments.

Deprecation lineage is recorded as a directed acyclic graph linking each version to its predecessors and successors. Operators configure retention parameters governing how long deprecated versions remain in the active registry before being archived to a cold storage tier. Archival does not delete; it relocates definitions to a substrate optimized for infrequent access while preserving cryptographic accessibility through the registry's content-addressed index. Audits across version boundaries traverse the lineage graph, retrieving definitions on demand from whichever tier holds them.

Cross-version compatibility audit produces a structured report identifying, for each pair of versions present in a population of objects, the compatibility entry consulted, the migrations applied, and any violations detected. Audit cadence is configurable, ranging from continuous streaming audit in high-assurance deployments to periodic batch audit in lower-assurance contexts. The audit output is itself recorded in an append-only lineage structure cryptographically chained to the registry state, supporting independent verification by third parties.

Alternative Embodiments

The policy registry may be embodied as a centralized append-only log under a designated authority, as a federated set of replicated logs operated by independent authorities, or as a fully decentralized ledger anchored in a public or consortium substrate. The centralized embodiment minimizes operational complexity and is appropriate when a single trust root is acceptable. The federated embodiment supports multi-party governance with quorum-based publication. The decentralized embodiment supports adversarial or jurisdictionally heterogeneous deployments and uses substrate-native commitment to anchor registry integrity.

The compatibility relation may be embodied as an explicit table indexed by version pairs, as a procedural function that generates compatibility entries on demand from version metadata, or as a hybrid in which a default procedural rule is overridden by explicit entries where required. The explicit-table embodiment maximizes auditability; the procedural embodiment minimizes registry size; the hybrid embodiment balances the two and is preferred in large deployments with regular incremental version publication.

Object policy references may be embodied as inline version identifiers, as cryptographic pointers to registry entries, or as hierarchical references combining a policy family identifier with a version selector. Inline identifiers are simplest and adequate for closed populations. Cryptographic pointers prevent version drift and support cross-substrate object portability. Hierarchical references support multi-policy ecosystems in which a single object may reference distinct versions of multiple orthogonal policies.

Migration projections may be embodied as declarative field-mapping specifications, as content-addressed precompiled WebAssembly modules, or as state machines synthesized from formal version-difference specifications. Declarative specifications are most auditable and admit formal verification. Precompiled modules maximize execution efficiency and are preferred when migration occurs on a hot path. Synthesized state machines are appropriate when the version-difference language is rich enough to admit synthesis and the deployment values structural correctness over expressive flexibility.

Composition With Adjacent Mechanisms

Versioned policies compose with structural validation, lineage tracking, and cross-substrate object portability to produce a coherent agent schema. Structural validation consults the policy version referenced by each object, ensuring that constraints applied at validation time match the constraints in force when the object was authored. Lineage tracking records the policy version under which each state transition was evaluated, supporting retrospective audit even when the policy registry has since evolved. Cross-substrate portability requires that policy references travel with objects across substrate boundaries; the content-addressed identifier embodiment supports this requirement directly.

The mechanism also composes with revocation and access control primitives that operate at the agent level. A revoked credential's authorized scope may be expressed in terms of policy versions, allowing scope to evolve as policies evolve without requiring credential reissuance. Access control predicates may consult policy versions as part of their precondition logic, supporting fine-grained version-aware authorization decisions. These compositions extend the schema layer's structural guarantees into adjacent governance primitives without compromising the determinism or auditability of either.

Composition with multi-policy ecosystems is supported by hierarchical policy references in which an object may declare versions for multiple orthogonal policy families simultaneously. A given object might bind to version seventeen of an identity policy, version four of a financial-transaction policy, and version twenty-two of a privacy-disclosure policy. Validation walks each declared reference independently and aggregates the results into a single structural validity decision. Cross-family compatibility relations may also be defined where families interact, supporting evolution of one family without requiring synchronized evolution of orthogonal families that nevertheless share objects in common.

The mechanism additionally composes with substrate-level replication and conflict resolution. Because policy definitions are content-addressed and append-only, replicating the registry across substrates reduces to replicating an immutable key-value store, which is straightforward and admits standard CRDT or gossip-based protocols. Cross-substrate object portability is supported because policy references are themselves content-addressed: an object referencing policy digest H validates against any registry that contains the entry at H, regardless of which substrate hosts the registry. This decouples object portability from registry topology and allows policy ecosystems to span administrative boundaries without requiring federation agreements at the registry level.

Distinction From Prior Art

Conventional schema versioning approaches in distributed systems, including protocol buffer schema evolution, Avro schema resolution, and JSON Schema $id-based versioning, address compatibility at the wire-format level. They typically support adding optional fields, deprecating fields by tag, and renaming fields through aliases. These approaches do not, however, embed policy references in the objects themselves at the level of structural identity; they treat schema as external metadata that the receiver must obtain through a separate channel. The disclosed mechanism differs by binding the policy reference into the object's identity digest, making schema mismatch structurally detectable rather than merely a runtime warning.

Database migration frameworks address schema evolution at the storage level through migration scripts and version metadata. They typically require synchronized upgrades across the population and treat migration as a discrete event. The disclosed mechanism supports asynchronous coexistence of multiple policy versions across a heterogeneous population, with cross-version interaction mediated by an explicit compatibility relation rather than by population-wide synchronous migration. This is appropriate for federated and decentralized deployments in which synchronized upgrades are not feasible.

Semantic web ontology versioning, including OWL imports and PROV-O versioning, addresses ontological evolution but does not provide a deterministic compatibility relation, an append-only registry binding, or cryptographic identity for policy references. The disclosed combination of versioned registry, content-addressed policy reference, restricted total-function migration language, and cryptographically chained audit lineage is novel and is not anticipated by the surveyed prior art.

Disclosure Scope

The disclosure encompasses the versioned policy registry as an append-only content-addressed structure, the embedding of policy references in object identity, the deterministic compatibility relation between version pairs, the restricted projection language for migrations, the deprecation lineage graph, the cross-version compatibility audit procedure, and the alternative embodiments of registry, relation, reference, and projection described above. The disclosure further encompasses the composition of versioned policies with structural validation, lineage tracking, and substrate-portable object identity as integral architectural properties of the agent schema layer.

The scope expressly excludes embodiments in which policy versions are mutable after publication, in which policy references are not bound to object identity, in which compatibility procedures are non-deterministic or environment-dependent, or in which deprecation silently invalidates extant objects. These exclusions are structural and are enforced by the type system of the schema layer rather than by operational convention. They are what render the disclosed mechanism a primitive supporting cross-version structural interoperability rather than merely a versioning convention layered atop conventional infrastructure.