In legacy identity systems, this coordination challenge was typically solved through:

• Centralized schema repositories: Organizations like schema.org provided canonical schema definitions
• Namespace allocation authorities: Similar to DNS or URI schemes, central bodies allocated namespace prefixes
• Registry-based discovery: Verifiers could query central registries to retrieve schema definitions
• Version management: Central authorities coordinated schema evolution and versioning

This centralized approach created several dependencies:

• Trust in registry operators: Participants must trust the central authority's governance
• Availability requirements: The registry must remain accessible for schema resolution
• Coordination overhead: Schema changes require registry updates and coordination
• Single points of failure: Registry outages impact the entire ecosystem

KERI's Approach

The ACDC (Authentic Chained Data Container) protocol fundamentally transforms the schema namespace registry concept through its use of directed acyclic graphs (DAGs). This architectural innovation decentralizes the traditional centralized registry model while maintaining—and enhancing—interoperability.

Decentralization Through Graph Architecture

ACDC's graph-based approach eliminates the need for centralized namespace coordination by embedding schema relationships directly into the credential structure itself. Each ACDC contains:

• SAIDs (Self-Addressing Identifiers) that cryptographically bind schema definitions to their content
• Edge properties that define relationships between ACDCs in the graph
• Chained provenance that creates verifiable schema lineage without central coordination

The directed acyclic graph structure ensures that schema relationships are:

• Cryptographically verifiable: Each schema's SAID provides content-addressable integrity
• Self-describing: Schema definitions are embedded in the credential structure
• Composable: Schemas can reference and build upon other schemas through graph edges
• Decentralized: No central authority is required to resolve or validate schema relationships

Interoperability by Design

ACDC achieves what traditional schema namespace registries attempted through centralization, but does so through cryptographic data structures:

1. Content-addressable schemas: The SAID of a schema definition serves as its globally unique identifier, eliminating namespace collision concerns

2. Verifiable schema chains: The DAG structure creates authentic provenance chains for schema evolution and derivation

3. Distributed discovery: OOBI (Out-Of-Band Introduction) enables decentralized schema discovery without registry queries

4. Cryptographic binding: Schemas are bound to AIDs (Autonomic Identifiers) through KEL (Key Event Log) anchoring, providing verifiable authorship

This approach transforms schema interoperability from an organizational coordination problem into a cryptographic verification problem. Instead of trusting a central registry to maintain namespace uniqueness and schema definitions, verifiers can cryptographically verify schema integrity and provenance directly from the ACDC structure.

Governance Without Centralization

While ACDC eliminates the need for centralized technical infrastructure, it does not eliminate governance. Organizations can still establish governance frameworks for schema usage, but these frameworks operate through:

• Delegated authority: Schema governance can be delegated through KERI's delegation mechanism
• Verifiable policies: Governance rules can be expressed as verifiable credentials themselves
• Distributed enforcement: Policy compliance is verified cryptographically rather than enforced centrally

The vLEI (verifiable Legal Entity Identifier) ecosystem demonstrates this approach, where GLEIF establishes governance frameworks for credential schemas without operating a centralized schema registry. Instead, schema definitions are distributed through the ACDC graph structure and verified through cryptographic means.

Practical Implications

Use Cases

The transition from centralized schema namespace registries to ACDC's graph-based approach impacts several key use cases:

Enterprise credential ecosystems: Organizations issuing credentials no longer need to coordinate with a central registry. They can define schemas, publish them through OOBI, and rely on cryptographic verification for interoperability.

Cross-organizational credentials: When credentials need to reference schemas from multiple organizations, the DAG structure enables verifiable composition without requiring all parties to register with a common authority.

Schema evolution: Organizations can evolve their schemas over time, with the DAG structure maintaining verifiable lineage from original to derived schemas without central version management.

Regulatory compliance: In regulated industries like finance (vLEI) or healthcare, schema governance can be enforced through verifiable policy credentials rather than registry access controls.

Benefits

ACDC's approach to schema management provides several advantages over traditional namespace registries:

1. Elimination of single points of failure: No central registry means no registry outages or availability concerns

2. Reduced coordination overhead: Schema publishers don't need approval or registration with central authorities

3. Enhanced privacy: Schema resolution doesn't require queries to central services that could track usage patterns

4. Cryptographic verifiability: Schema integrity and provenance are mathematically verifiable rather than trust-based

5. Scalability: The decentralized architecture scales horizontally without central bottlenecks

6. Censorship resistance: No central authority can prevent schema publication or revoke namespace allocations

Trade-offs

While ACDC's approach provides significant benefits, it also introduces considerations:

Discovery complexity: Without a central registry, discovering relevant schemas requires alternative mechanisms like OOBI or community-maintained directories

Governance challenges: Establishing and enforcing schema governance without central authority requires new organizational patterns and tooling

Learning curve: Developers familiar with traditional registry-based systems must understand graph-based schema relationships and cryptographic verification

Tooling maturity: The ecosystem of tools for managing decentralized schema graphs is still evolving compared to established registry-based systems

Despite these considerations, ACDC's graph-based approach represents a fundamental architectural improvement that aligns schema management with KERI's broader principles of decentralization, cryptographic verifiability, and autonomic operation. The elimination of centralized schema namespace registries removes a significant trust dependency while maintaining—and enhancing—the interoperability that such registries were designed to provide.