On improving efficiency of model checking through systematically ...

fixed point can be reached without further analysis on every values of x>1.
On the contrary, Uppaal does not employ such abstraction. Integer values
are handled exactly as they are and thus the fixed point equation can be
infinite. A detailed explanation of fixed point theory and its application in
model checking is presented in the research report[16].
The original models of the four systems described in this chapter are
not the same source; They were initially specified in Nbac, PMC/Uppaal, and
Lustre [2] input language. All of them are however eventually transformed
into Nbac input language. Therefore, it is possible that the original model
is simple but the Nbac output model is complicated due to transformation
and abstraction steps. We categorize these systems based on output models
from Nbac which are inputs for verification done by PMC or Uppaal.
Practical models of the case studies in text format can be found in the
Appendix section.
4.1 The tiny example
The tiny example is taken from Nbac tutorial[21]. This simple system has
two counters x, y which are alternatively incremented. It is represented by
the automaton shown in Figure 4.1.
init
init := false
ok := true
x := 0
y := 0
¯b0 ¯b1
x ≥ yx := x +1
b 0 ¯b1
x