Schemas & Semantic Layer

Communication Schemas & Semantic Layer

In open multi-agent systems, message exchange without agreed semantics is noise.
Different agents may be built by different teams, run in different domains, and evolve at different speeds. Without a shared semantic layer, the network degrades into a set of incompatible dialects.

The Semantic Plane in OpenMesh exists to ensure that meaning is preserved, validated, and extended across this diversity, while allowing incremental evolution without systemic breakage.

Self-Describing Messages

• In OpenMesh, every message is a self-contained unit of meaning — carrying not only its payload but also the semantic, structural, and procedural context required to interpret it.

• This approach removes the need for out-of-band assumptions or hardcoded protocol logic, enabling agents that have never interacted before to still understand, validate, and respond appropriately to each other.

• Embedded Semantic Metadata

• Each OpenMesh message contains embedded metadata fields that explicitly link it to:

  • Versioned Schema URI: Defines the expected structure, data types, and constraints for the payload.
  • Protocol Definition URI: Points to the procedural or state machine definition governing how the message should be interpreted in the context of an interaction.
  • Protocol Versioning: Specifies the exact protocol version to ensure compatibility negotiation.
  • Security Annotations: Digital signatures, sender DID, encryption metadata, and access control tags.

• Capabilities Enabled by Self-Describing Messages

• Schema Validation Before Processing

  • The recipient retrieves the referenced schema from the Distributed Schema Registry.
  • Payload is validated against the schema to ensure type safety and adherence to expected structure.

• Protocol Context Awareness

  • Knowing the protocol URI allows the recipient to position this message within the correct state machine or procedural flow.
  • This prevents misinterpretation and supports multi-step workflows.

• Version Negotiation

  • If the exact protocol version is not supported, the agent can:
  • Attempt fallback to a compatible minor version.
  • Initiate schema/protocol negotiation.
  • Use a protocol bridge or schema translator to adapt the message.

• Semantic Rejection for Safety

  • If the schema is unknown, deprecated, or flagged as untrusted, the agent can reject the message before any unsafe processing occurs.
  • Rejection can be accompanied by a reject reason and, optionally, a suggested compatible schema.

Distributed Schema Registry

• The Schema Registry is the semantic backbone of OpenMesh.

• It ensures that every message, topic, and protocol in the network can be unambiguously interpreted, validated, and evolved over time regardless of where the communicating agents originate or how they are implemented.

• In an open MAS, where heterogeneity and independent evolution are the norm, the Schema Registry plays the same role that a standards body plays in human societies — defining and preserving the “language” agents use to cooperate.

• Federated, Content-Addressable Store

• The Schema Registry operates as a federated network of independently managed nodes that collectively store:

  • Message Schemas: Formal definitions of payload structure, data types, and allowed values.
  • Protocol Definitions: Descriptions of multi-step interactions, including state machines and procedural codes.
  • Compatibility Rules: Declarations of backward, forward, or incompatible changes between versions.

• Each stored artifact is content-addressed: its URI includes or resolves to a cryptographic hash of its contents, ensuring immutability and integrity verification. Any agent can verify that the schema it retrieved is exactly the one the sender referenced, with no possibility of silent tampering.

• Discoverability via Directory Nodes

• All registry nodes are discoverable through Directory Nodes, which:

  • Publish registry endpoints and supported namespaces.
  • Allow agents to locate the nearest or most trusted registry instance.
  • Enable agents to select registries based on policy, jurisdiction, or trust anchors.

• This ensures that schema resolution is fast, context-aware, and policy-compliant.

• Replication Across Operators

• To ensure resilience and avoid dependence on any single operator:

  • Horizontal Replication: Multiple registry nodes mirror the same schemas to guarantee availability.
  • Namespace Delegation: Each domain can operate its own registry for domain-specific schemas while federating with others for global interoperability.
  • Consistency Protocols: Registries synchronize updates via a gossip-based schema replication protocol or signed update feeds to maintain integrity across mirrors.

• Key responsibilities:

• Store versioned schemas with immutable hashes.
• Publish compatibility declarations (backward, forward, or none).
• Host protocol state machine definitions for higher-order interactions.

• Maintain deprecation notices and migration hints.

• Why Federated?

• Centralizing schema hosting under a single operator would create a semantic chokepoint — a risk to resilience, governance independence, and network neutrality.

• By federating the Schema Registry:

  • Domains retain control of their own schemas, governance rules, and update policies.
  • Global discoverability is preserved through federation protocols and Directory Node indexing.
  • Interoperability is strengthened, as schemas are still globally resolvable even when maintained by independent entities.
  • Trust diversity is supported — agents can choose registries based on jurisdiction, operator reputation, or cryptographic attestations.

Protocol Definition and State Machines

• Beyond single messages, complex interactions in OpenMesh require structured protocols that govern how agents converse, when they transition states, and under what rules they conclude an interaction.

• Performative-Verbs Layer

• At the base level, OpenMesh supports a minimal, FIPA-inspired set of performative verbs such as inform, request, propose, `agree, refuse, query, cancel, and confirm which define the intent behind each message.
  This provides a shared signaling vocabulary that all agents can interpret, regardless of the higher-order process they belong to.

• Procedural Protocol Layer

• On top of performative verbs, OpenMesh supports procedural communication protocols — explicitly defined workflows that dictate the sequence, conditions, and branching logic of an interaction. These protocols are expressed as formal state machines or procedural code definitions, and may include:

  • Deterministic Sequences: Fixed step-by-step exchanges (e.g., authentication handshake, escrow release).
  • Branching Interaction Trees: Conditional paths depending on responses, context, or external triggers.
  • Timeout & Recovery Logic: Automated retries, fallback paths, and safe abort mechanisms.
  • Embedded Execution Logic: Procedural rules that execute code blocks (e.g., calculation, validation, or policy checks) mid-protocol.
  • Deliberate Codes: Predefined, domain-specific “interaction codes” that encapsulate common procedures (e.g., market clearing, multi-party vote tallying, swarm maneuver coordination). These codes are versioned and registered in the Schema Registry, ensuring reproducibility and trust across domains.
  • Mixed-Layer Execution: Combining procedural rules with social-layer constraints (e.g., only accept proposals from trusted circle members above a reputation threshold).

• Why Procedural Protocols Matter for Open MAS:

• Allow repeatable, auditable interactions that transcend informal signaling.
• Encode domain knowledge directly into communication workflows, making them self-enforcing and less error-prone.
• Enable cross-domain interoperability when deliberate codes are shared, registered, and versioned in the Schema Registry.
• Provide a path to automated compliance - agents can follow procedural protocols to ensure messages are both syntactically valid and procedurally lawful.

Schema and Protocol Negotiation & Translation

• In an open MAS like OpenMesh, it is inevitable that agents will encounter messages encoded in schemas or protocols they do not currently support.

• Agents are developed independently, evolve at different rates, and may join the network years after certain schemas or protocols have been introduced or even deprecated.

• To ensure that communication does not break in such cases, OpenMesh defines a negotiation-first, translation-enabled process for achieving semantic interoperability on demand.

• Negotiation Workflow

• When an agent receives a message referencing an unknown or unsupported schema or protocol:

  1. Registry Lookup
  2. The agent queries the Distributed Schema Registry for the URI provided in the message metadata.

  3. The registry returns the schema or protocol definition along with version history and compatibility declarations.

  4. Compatibility Check

  5. If the schema/protocol is compatible with the agent’s capabilities (as per registry metadata), the agent proceeds with validation and processing.

  6. Compatibility includes backward (can process older messages) and forward (can process newer messages) checks.

  7. Fallback to Closest Compatible Version

  8. If exact compatibility is not available, the agent selects the closest compatible version.

  9. Meta-Protocol Negotiation

  10. If no direct compatibility exists, the agent initiates a meta-protocol negotiation — a higher-order interaction where the sender and receiver attempt to agree on an alternative schema or protocol they both support.

  11. This negotiation can result in switching to an earlier version, a common intermediary schema, or a standardized compatibility protocol.

  12. Translation Path (Optional or Fallback)

  13. If negotiation fails or if a direct translation path is faster, the message is routed through a translator or protocol bridge.

• Translator / Protocol Bridge Functions

• A translator (also called a protocol bridge) is a specialized network participant — either an agent, relay extension, or dedicated service that transforms messages between incompatible schemas or protocols.

• Capabilities include:

  • Schema Translation
  • Maps fields, types, and semantics from the unknown schema to one understood by the recipient.
  • Preserves meaning, intent, and constraints wherever possible.

  • Applies default values or semantic approximations when perfect fidelity is not possible.

  • Protocol Mediation

  • Acts as an interpreter between incompatible protocol state machines.
  • Ensures that state transitions, performative verbs, and timeouts are mapped to equivalent constructs in the target protocol.

  • Handles procedural differences e.g., inserting additional handshake steps if the target protocol requires them.

  • Cross-Version Wrapping

  • Encapsulates a newer protocol’s payload in a backward-compatible envelope for legacy agents.

  • Allows older agents to at least receive and store newer messages even if they cannot natively process all fields.

  • Multi-Hop Interpretation

  • Enables transitive compatibility by chaining translators:
    • Schema X → Schema Y via one bridge
    • Schema Y → Schema Z via another
  • Useful when no direct X → Z translator exists, but intermediate mappings do.

• Discovery and Advertising of Translators

• Discoverability: Translators are indexed by Directory Nodes and advertise:
  • Supported transformations
  • Latency and throughput profiles
  • Trust attestations or cryptographic proofs
  • Domain-specific constraints (e.g., may only translate within certain namespaces or for specific circles)
• Operation: Translators may be run by:
  • Domain operators (ensuring local policy compliance)
  • Independent service providers (offering translation as a utility service)
  • Agents themselves (self-hosted compatibility modules for private workflows)
• Why Translation Agents Matter for Open MAS
• In an open, evolving multi-agent ecosystem:
  • Longevity: Legacy agents remain functional even after newer protocols and schemas emerge.
  • Interoperability Across Divergent Ecosystems: Domains with their own protocol dialects can still cooperate without forcing wholesale migration.
  • Reduced Upgrade Burden: Agents can adopt newer schemas incrementally, relying on translators for interim compatibility.
  • Network Cohesion: Prevents fragmentation into isolated protocol “islands” that cannot communicate.
  • Adaptive Interoperation: Translators can be dynamically deployed to connect emerging subnets, experimental domains, or specialized agent groups.

Validation at Ingress & Egress

• In OpenMesh, every message that flows through the network — whether between agents, relays, or other components — undergoes strict validation at both ingress (incoming) and egress (outgoing) points.
  This ensures that malformed, unauthorized, or semantically inconsistent messages are intercepted before they can cause harm or disrupt coordination.

• Ingress Validation

• Applied at the entry point of any relay, gateway, or agent endpoint.
• Checks that each inbound message matches the declared schema and adheres to the relevant policy rules before it is accepted for processing.
• Prevents protocol violations, schema mismatches, or malicious injection from entering the system.

• Common use cases include stopping unapproved message types, rejecting incomplete payloads, and verifying protocol state transitions before they propagate.

• Egress Validation

• Applied at the exit point before a message leaves a node or component for transmission to others.
• Confirms that outbound messages are well-formed, schema-compliant, and protocol-valid before they are sent into the network.
• Prevents unintentional leakage of internal, malformed, or partial data.

• Acts as a last safeguard before a message crosses trust boundaries.

• Failure Handling

• All validation failures are logged in detail, including precise rejection reasons (e.g., schema mismatch, DSL violation, protocol error).
• Optionally, these failure logs can be published to a dedicated audit topic for network-wide transparency and forensic analysis.
• This enables downstream observability tools to detect systemic issues, replay failures for debugging, and maintain accountability in multi-party interactions.

Semantic Security

• Semantic security extends beyond encryption and transport-level safety.

• It controls the meaning and permissible use of messages based on their declared structure, type, and protocol context.

• Key Measures

• Schema Whitelists/Blacklists

  • Explicitly allow or deny certain message types from crossing defined trust boundaries.
  • Prevents untrusted agents or domains from injecting prohibited message categories (e.g., financial commands, privileged control messages).

• Schema-bound Access Control Lists (ACLs)

  • Enforces access control at the message type level, not just at the broader topic or channel level.
  • Example: An agent may be allowed to publish market/proposal@v1.0.0 messages but denied permission to send market/contract@v2.0.1 messages.

• Protocol Enforcement

  • Ensures that messages respect the defined state machine of a protocol.
  • Disallows messages that are out-of-order, invalid for the current negotiation stage, or violating declared constraints.
  • This prevents logical exploitation or state desynchronization between agents.

• Benefits for Open MAS

• By embedding schema URIs and protocol references directly in every message, OpenMesh delivers long-term semantic stability for heterogeneous, evolving agent ecosystems.

• Key Benefits

  • Cross-Domain Meaning Preservation
  • Messages retain their intended meaning even when different agents use different internal data models.

  • Schema acts as a shared “semantic anchor” across trust boundaries.

  • Graceful, Non-Disruptive Upgrades

  • Agents can upgrade to new schemas and protocols gradually, without causing mass communication failures.

  • Mixed-version interactions remain possible during migration periods.

  • Support for Heterogeneous Agent Ecosystems

  • Works across different agent architectures, programming languages, and runtime environments.

  • Enables collaboration between legacy agents and cutting-edge AI systems over decades.

  • Prevention of Semantic Drift

  • Avoids the gradual misalignment of meaning that would otherwise fragment the MAS into isolated, incompatible clusters.
  • Maintains a coherent global semantic fabric despite continuous evolution.