Event Feed API for change notifications

[gataka]

What is missing?

The AAS specification currently lacks a standardised mechanism for consumers to be notified about changes to Assets, AAS, or Submodels without polling the full AAS Data API repeatedly.

A lightweight, HTTP-based Event Feed API would fill this gap: a single GET /events endpoint returns a paginated, cursor-based feed of change events (CloudEvents envelope format) that consumers can poll incrementally. Consumers choose between a COMPACT (identifier-only) and FULL (complete payload) presentation mode, can filter by event type and data-level fields (e.g. data.semanticId.keys[*].value), and discover server capabilities via a well-known endpoint (/.well-known/event-feed.json).

The event types are versioned (io.admin-shell.asset.created.v1) and the payload schemas (dataschema) are aligned with the AAS metamodel — using ModelReference, ModelReference, and the AAS Reference object for semantic IDs.

How should it be fixed?

A new specification for an Event Feed API should be added to the AAS API suite, covering:

• GET /events endpoint with cursor-based pagination, limit, since, and filter (RSQL) query parameters
• CloudEvents-compatible record structure with lowercase attribute names (dataschema, type, subject, source)
• COMPACT and FULL presentation modes with matching dataschema URLs
• Three built-in event types: assetChangeEvent, aasChangeEvent, submodelChangeEvent — each with FULL and COMPACT JSON Schema variants aligned to the AAS metamodel
• Capabilities discovery via /.well-known/event-feed.json

This concept is the result of the corporation of Phoenix Contact, EPLAN and INNOQ.

The complete concept and all data schemas are attached:

Attachments:

• events-feed-rfc.pdf — Specification of the Event Feed API

• openapi-events.yaml — OpenAPI 3.x description of the GET /events and GET /.well-known/event-feed.json endpoints

• metamodel-assetChangeEvent.v1.schema.json — JSON Schema (FULL) for asset change events; references use ModelReference<AssetAdministrationShell> and ModelReference<Submodel>

• metamodel-assetChangeEventCompact.v1.schema.json — JSON Schema (COMPACT) for asset change events; minimal payload carrying only globalAssetId

• metamodel-aasChangeEvent.v1.schema.json — JSON Schema (FULL) for AAS change events; submodel references use ModelReference<Submodel>

• metamodel-aasChangeEventCompact.v1.schema.json — JSON Schema (COMPACT) for AAS change events; minimal payload carrying only aasId

• metamodel-submodelChangeEvent.v1.schema.json — JSON Schema (FULL) for submodel change events; semanticId is represented as an AAS Reference object

• metamodel-submodelChangeEventCompact.v1.schema.json — JSON Schema (COMPACT) for submodel change events; minimal payload carrying submodelId and semanticId as Reference

• submodelChangeEvent.v1.schema.json — JSON Schema (FULL) for submodel change events; simplified variant with semanticId as plain URI string (included for comparison)

• submodelChangeEventCompact.v1.schema.json — JSON Schema (COMPACT) for submodel change events; simplified variant (included for comparison)

• [ x] I have signed the required Developer Certificate of Origin (DCO) already.

[sebbader-sap]

See #41 and #297