Event Bus — Conceptual Overview
Audience: Implementers, Architects, Runtime Authors Governance Rule: DGP-30
1. What Event Bus Refers To
Event Bus in MPLP refers to the observability and coordination dimension that concerns event routing across protocol layers. It is the conceptual area where lifecycle events, observability data, and integration signals intersect.
Event Bus is not a specific technology (like Kafka or RabbitMQ). It is an abstraction boundary that implementations address with technology-specific solutions.
2. Conceptual Areas Covered by Event Bus
Event Bus concerns the following areas:
| Conceptual Area | Description |
|---|---|
| Event Routing | Relates to delivering observability events to interested parties |
| 12 Event Families | Concerns the structured event taxonomy |
| Required Events | Relates to pipeline_stage and graph_update semantics |
| L4 Integration | Is involved in ingesting file, git, CI, and tool events |
| Event Ordering | Concerns causality preservation across event streams |
3. What Event Bus Does NOT Do
Event Bus explicitly does not:
- ❌ Define specific messaging protocols (AMQP, MQTT, etc.)
- ❌ Mandate persistent vs. ephemeral delivery
- ❌ Prescribe exactly-once vs. at-least-once semantics
- ❌ Define event retention policies
- ❌ Constitute a message queue implementation
4. Where Normative Semantics Are Defined
The normative semantics related to Event Bus are NOT defined on this page.
They are distributed across:
| Normative Source | What It Covers |
|---|---|
Event Core Schema (mplp-event-core.schema.json) | Base event structure, 12 families |
| Pipeline Stage Event Schema | Lifecycle transition event structure |
| Graph Update Event Schema | PSG change notification structure |
| Observability Invariants | 12 rules for event structure |
| L3 Execution & Orchestration | Event emission semantics |
5. The 12 Event Families (Reference)
| Event Family | Required | Conceptual Purpose |
|---|---|---|
pipeline_stage | YES | Relates to Plan/Step lifecycle transitions |
graph_update | YES | Concerns PSG structural changes |
import_process | No | Relates to project initialization |
intent | No | Concerns user request capture |
delta_intent | No | Relates to intent modifications |
methodology | No | Concerns approach selection |
reasoning_graph | No | Relates to chain-of-thought traces |
runtime_execution | No | Concerns LLM/tool execution details |
impact_analysis | No | Relates to change impact predictions |
compensation_plan | No | Concerns rollback strategies |
cost_budget | No | Relates to token/cost tracking |
external_integration | No | Concerns L4 system events |
6. Conceptual Relationships
Event Bus interacts with the following protocol elements:
7. Reading Path
To understand Event Bus-related normative semantics, read:
- Observability Overview — Event taxonomy
- Event Taxonomy — Detailed event definitions
- L3 Execution & Orchestration — Runtime behavior
- L4 Integration Infrastructure — Integration event routing
Governance Rule: DGP-30 See Also: Event Bus Anchor (Normative)