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**Modular Modeling of Large-Scale Systems using Communicating
X-Machines**

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P. Kefalas, G.Eleftherakis
and E.Kehris

**Abstract: **A X-machine is a general computational
machine that unlike a finite state machine (FSM) can model non-trivial
data structures as a typed memory tuple. In addition, a X-machine models
the dynamic part of a system by employing transitions, which are not labeled
with simple inputs but with func-tions that operate on inputs and memory
values. The X-machine formal method is valuable to software engineers since
it is rather intuitive, while at the same time formal descriptions of data
types and functions can be written in any known mathematical notation.
These differences allow the X-machines to be more expressive and flexible
than the FSM. A set of X-machines can be viewed as components, which communicate
with each other in order to specify larger systems. This paper describes
a methodology of building communicat-ing X-machines from existing stand-alone
X-machine models. It is suggested that the development of complex systems
can be split into two separate activi-ties: (a) the modeling of stand-alone
X-machine components and (b) the description of the communication between
these components. The approach is disciplined, practical, modular and general
in the sense that it subsumes the existing methodologies. The proposed
methodology is accompanied by an ex-ample, which demonstrates the use of
communicating X-machines towards the modeling of large-scale systems.
**Keywords: -**

**Appeared in: WORKING PAPER**

**Available: -**

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