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This concept has the following major specialisations within the Foundation package:
plus numerous specialisations in other packages, notably (for present purposes):
The Foundation package is concerned with establishing a basic 'physics' for a MESSAGE model. The 'world' of a MESSAGE model is made up of instances of concrete and behavioural entities (activities). These are described elsewhere. For present purposes, what matters is that at a point in time each of these is in a particular state. The state of the world is the combination of the states of the instances. Changes in state (and also creation and destruction) of the instances are caused by execution of Actions, which occur at discrete points in time. The effects of actions are observed as Events. Thus the evolution of the world can be completely described by a snapshot of the world at a point in time, plus a history of all events. However, it is not practical to work with explicit desciptions of the world and its history at this microscopic level of detail. Accordingly the concept of Situation is introduced as a means of describing the world at a macroscopic level. A Situation is a partial description (in terms of constraints on the world state and past history) at a point in time, and hence corresponds to a set of possible (micro-)states.
The TimePoint specialisation of MESSAGE-entity embraces concepts that refer to a particular point in time. An InformationEntity is a quantum of information about the world state history.