On improving efficiency of model checking through systematically ...

When applying the abovementioned procedure to implement nbac2xtgxml,
we faced the following problems:
1. As explained in Section 3.2, expressions have to be split into atomic
elements in PMC models. In the implementation, we had to write procedures
to parse expressions obeying the precedent rule on operators.
2. PMC does not support Boolean operations on Boolean type variables.
Therefore, Nbac Boolean variables are saved as integer variables in
PMC model. The Boolean expression “b and not c”, in which b,c are
Boolean variables, is specified in PMC model as “b==1 and c==0”.
3. Since PMC neither supports Boolean type variables nor returns Boolean
values for comparison expressions, if-then-else statement in assignments
cannot be modeled as described in Section 3.3. A number of
extra locations and transitions have to be added to model assignments.
Consider a set of assignments for a transition in the following example:
x:= if a then x1 else if b then x2 else 0;
y:= if c then y1 else if d then y2 else 0;
z:= if e then z1 else if f then z2 else 0;
Figure 3.11 shows how the transition is modeled in Uppaal.
x := a*x1 + b*x2;
y:=c*y1+d*y2;
z:=e*z1+f*z2;
s 0 s 1
Figure 3.11: Modeling assignments in Uppaal
Figure 3.12 shows how the transition is modeled in PMC.
a==1
c==1
e==1
x:=x1 y:=y1 z:=z1
s 0 s 1
b==1
x:=x2
d==1
y:=y2
f==1
z:=z2
Figure 3.12: Modeling assignments in PMC
Modeling assignments this way adds a large amount of transitions and
locations to the PMC model. However, we had no other choice to solve
this problem.
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