On improving efficiency of model checking through systematically ...

achieve a more efficient model checker by combining Nbac and PMC. Onthe
one hand, Nbac and PMC share the same idea of partition refinement in the
sense that in both algorithms the starting point is a very coarse partition of
the state space then the partition is analyzed and refined until termination.
On the other hand, they are very different from each other in computation
method and typical systems they deal with.
The study on Nbac and PMC leads to a proposed approach to combine
them in a systematic way to improve efficiency of model checking for a class
of models. In the research report, we express our idea of a systematic combination
and leave the implementation and evaluation of our approach for
the second phase, the thesis project. The report also includes an experiment
on Fischer’s protocol and some remarks on model checking in practice.
1.3 Objectives
The ultimate goal of our project is to improve efficiency of model checking
by systematically combining tools in a reasonable way. We utilize Nbac as a
tool to bring abstraction capability to PMC/Uppaal 1 through a systematic
approach. In our approach, the original system model is put into Nbac.
Then, Nbac generates an abstract model based on abstract interpretation
framework. The output astract model is fed into a transformation tool to
be translated to an equivalent model that can be verified by PMC/Uppaal.
Figure 1.1 depicts this approach. By preprocessing the system model in this
way, we hope that we can obtain a smaller model for which verification by
PMC/Uppaal is feasible.
In Figure 1.1, the dashed box contains the transformation step which is
taken by a tool. This tool does not only translate the syntax but also assures
the semantics equivalence between an Nbac-like 2 model and a PMC/Uppaallike
model. We characterize a PMC/Uppaal-like model as an XTG 3 model
for the sake of generality. An XTG model is a timed automata[7] extended
with the notion of urgency and the synchronous communication mechanism.
Due to the considerable size of an Nbac-like abstract model, the transformation
process is very complicated and thus cannot be done manually.
Therefore, the development of such a transformation tool is essential. Fur-
1 Uppaal [8] was not involved in our project in the beginning. After quite a long time
working with PMC, we eventually found that PMC was not suitable in our approach for some
reasons explained later on. Therefore, we have chosen Uppaal to replace PMC to proceed
with our project.
2 called “Nbac model” for short later on
3 Extended Timed Graph
4