The behavior of a given DEVS model is a set of sequences of timed events including null events, called event segments, which make the model move from one state to another within a set of legal states.
To define it this way, the concept of a set of illegal state as well a set of legal states needs to be introduced.
In addition, since the behavior of a given DEVS model needs to define how the state transition change both when time is passed by and when an event occurs, it has been described by a much general formalism, called general system [ZPK00].
In this article, we use a sub-class of General System formalism, called timed event system instead.
Depending on how the total state and the external state transition function of a DEVS model are defined, there are two ways to define the behavior of a DEVS model using Timed Event System.
Since the behavior of a coupled DEVS model is defined as an atomic DEVS model, the behavior of coupled DEVS class is also defined by timed event system.
{\displaystyle {\mathcal {M}}=
is a Timed Event System
is the null event segment, i.e.
If unit event segment
, Computer algorithms to simulate this view of behavior are available at Simulation Algorithms for Atomic DEVS.
{\displaystyle {\mathcal {M}}=
is the null event segment, i.e.
, Computer algorithms to simulate this view of behavior are available at Simulation Algorithms for Atomic DEVS.
View1 has been introduced by Zeigler [Zeigler84] in which given a total state
In other words, the set of partial states is indeed
When a DEVS model receives an input event
in terms of the lifespan control, modellers have to update the remaining time in the external state transition function
is the same as the number of possible input events coming to the DEVS model, that is unlimited.
As a result, the number of states
is also unlimited that is the reason why View2 has been proposed.
If we don't care the finite-vertex reachability graph of a DEVS model, View1 has an advantage of simplicity for treating the elapsed time
every time any input event arrives into the DEVS model.
But disadvantage might be modelers of DEVS should know how to manage
View2 has been introduced by Hwang and Zeigler[HZ06][HZ07] in which given a total state
is computed as When a DEVS model receives an input event
in terms of the lifespan control, modellers can use
in nature, if the number of states, i.e.
is finite, we can draw a finite-vertex (as well as edge) state-transition diagram [HZ06][HZ07].
As a result, we can abstract behavior of such a DEVS-class network, for example SP-DEVS and FD-DEVS, as a finite-vertex graph, called reachability graph [HZ06][HZ07].