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Simulation is one of the most powerful tools for the planning, design,
and control of complex processes or systems.
Commercial simulators allow users
to find solutions by simulating their models representing the real system or
entity being modeled.
In such commercial simulators, numerous variables and
functions are pre-defined to support the users’ requirements, providing the
advantage of easy access and fast design for pre-defined types of models.
However, most commercial simulators have severe limitations modeling and
running complex real world systems. From the dynamic structural point of view,
the methods of adding or deleting a variable a component during simulation run-
time, are not provided because no command in the commercial simulators is
supported for such a specific behavior.
If they provide such a detailed
behavior, the number of commands including different parameter formats would
become too large and complex for users to easily seek appropriate commands.
For example, the number of the current commands in the SIMAN simulator, which
can not support the dynamic structural scheme, is too large--64 pages to
describe commands and variables--for users to look up. Therefore, limitation on
the practical number of commands and parameter formats of the commercial
simulators contains the expression of complex behaviors. Most commercial
simulators are incapable of extending the problem space or describing models
deeper than usual.
To overcome those limitations, it requires a methodology that provides
the flexibility to design and expandability to explode the problem space. As a
possible solution, DEVS (Discrete Event System Specification) environment is a
system-theory based simulation tool that provides expandability with modular
and hierarchical features, and flexibility with object-oriented messages as
user-defined data structures.
Based on system theory called the DEVS formalism
[1,2], the DEVS environment offers a library with which users can easily build
models in a hierarchical modular way.
In fact, the coupled model in DEVS
library is the major class to construct models hierarchically, while atomic
models are the most basic classes. Due to the hierarchical property, users can
quickly expand their models.
Since a message in DEVS environment carries an
object--the data structure defined by the user, information as a message type
can be delivered from one model to another. In other words, the size or scope
of the object can be determined by the user, and can be different from one
application to another, while the DEVS environment delivers the message
containing the object from a source model to a destination. (However, in DEVS-
JAVA, the user is responsible for creating and deleting the data structure in