Observer Models

Observer models describe how semantic observers are placed in the system graph.

At the structure level, an observer model defines placement, responsibility, logical execution context, and boundary participation for observation, interpretation, routing, hosting, projection, and event participation. This page describes structural use of the observer role, not the primitive definition of observer and not a specific runtime implementation.

Observer models may correspond to actors, services, request handlers, workflow activities, projection workers, process coordinators, entity command handlers, brokers, clients, schedulers, fibers, tasks, or infrastructure participants. Concrete mechanisms such as actor systems, HTTP pipelines, workflow engines, brokers, green-thread schedulers, or OS threads belong to substrate concerns such as actor systems, application hosts, workflow engines, brokers, and runtimes.

The same structural observer may be realized by different substrate contexts over time when the runtime preserves the logical execution context. Conversely, a single substrate mechanism, such as a worker thread, may realize many short-lived observers across different operations.

Observer models provide structure for:

Boundaries of interpretation.
Exogenous and endogenous event classification.
Command interpretation.
Routing and interaction.
Projection and hosting responsibilities.
Alignment between transition interpretation and the realization context that commits effects.