State

A state is the condition or configuration of a subject within a model boundary, modeled as an assignment of values to the subject's relevant dimensions at a time, version, or point in behavior.

Unlike an event, state is not occurrence-bearing. It represents what is relative to a subject, boundary, shape, and point of consideration, not what happened.

In Leslie Lamport's TLA formulation, a state is an assignment of values to variables: a mapping from variable names to values. In this model, those variables can be understood as the named dimensions made visible by a subject, boundary, shape, or specification.

State is not the same thing as the value used to read, write, transmit, or compare it. A value may represent all or part of state through a shape. An observation is a contextualized value produced by an observable acting on state.

The physics analogy is useful but informal: state is what observables act on to produce observations. Different observables may reveal different dimensions of the same underlying state.

State does not inherently carry identity, version, or lineage. Those belong to composite concepts such as entity state, observations, state records, histories, and provenance metadata.

For an entity, entity state is state attributed to an identity at a version. The version identifies the point in the entity history at which that state became current. Entity state is not merely a value with metadata; values represent, observe, persist, compare, or update entity state, while identity, version, and events locate it within an entity history. Entity state may be full or partial only relative to a declared shape, model boundary, or operation.

System state is broader than entity state. It may assign values across multiple subjects, observers, relations, stores, queues, processes, policies, and environmental dimensions inside a boundary. Observers interact with state by observing it and, when authorized, by interpreting input events as commands that may advance or mutate it through transitions.

In event-state duality:

Events carry occurrence, time, and change information.
States carry information and become current at a specific version or time.
For a sequential entity, state at version v is the result of applying the event that produced version v.
Events and states are dual views of behavior, not interchangeable representations.

External References

Leslie Lamport, The Temporal Logic of Actions, ACM Transactions on Programming Languages and Systems, 16(3):872-923, May 1994. Section 2.1 defines state in terms of assigning values to variables.