World Views

How to describe a simulation, or from what point of view to observe a simulation? There are a few popular modes. These are called world views.

event-scheduleing world view:

We view the simulation as a sequence of events scheduled according to their event time. The simulation is proceeded by a sequence of snap-shots of the system. Each snap-shot is triggered by a event from the event list.

Only one sanp-shot (the current one) is kept in computer memory. A new snap-shot can be derived only from the previous snap-shot, newly generated random variable values, and the event logic. Past snap-shots should be ignored when advancing the clock. The current snap-shot must contain all information necessary to continue the simulation.

We will see more examples later.

process-interaction world view:

In process-interaction world view, the simulation is considered as a collection of interactions among processes. It is similar to the object-oriented programming paradigm. Processes interact with each other by messages.

See Figure 3.4 on page 69 for an example. From the view point that two processes interact with each other.

Often specialized simulation package can support this view. These simulation packages take care of the time advancing issues for the programmers. Programming in general purpose high level language is difficult to use this process-interaction world view because it will be too complicated for programmers to specify all the details.

activity-scanning world view:

With activity-scanning approach, a modeler concentrates on the activities of a model and those conditions that allow an activity to begin. At each clock advance, the conditions for each activity are checked and if the conditions are true, the corresponding activity begins.

See Figure 3.4 on page 69 for an example. From the view point that activities and conditions.