On improving efficiency of model checking through systematically ...
On improving efficiency of model checking through systematically ...
On improving efficiency of model checking through systematically ...
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Since this case study is very small, the performance <strong>of</strong> verification was<br />
not our concern. Our goal was to see how the verification result would<br />
be. Uppaal could prove the safety property for the only abstract <strong>model</strong><br />
generated by Nbac.<br />
Although Uppaal could prove the safety property, it notified that “State<br />
discarded: Assignment to variable x is out <strong>of</strong> range”, meaning that Uppaal<br />
only proved the safety property for x was in the range <strong>of</strong> integer values. This<br />
warning may not cause too bad impact to the satisfaction <strong>of</strong> verification<br />
people because it is likely that the system is supposed to work for integer<br />
values only. Nevertheless, this fact could shed some light on the way Uppaal<br />
verified the system.<br />
5.2.2 Asynchronous reader/writer algorithm (aka Burn’s algorithm)<br />
The original <strong>model</strong> <strong>of</strong> this algorithm is specified in PMC input file burn simple<br />
2.xt. We constructed an Nbac input <strong>model</strong> for this algorithm from the PMC<br />
input <strong>model</strong> using the framework specified in Section 2.3. The resulting<br />
<strong>model</strong> is saved in file burn.ba. Nbac can generate 23 abstract <strong>model</strong>s for<br />
this algorithm.<br />
Uppaal gives a conclusive result for the safety <strong>of</strong> this system on the<br />
verification <strong>of</strong> the abstract <strong>model</strong> that contains 3 locations.<br />
Although we expected the system would not satisfy the property as<br />
proved by PMC, Uppaal proved that the safety property was indeed satisfied<br />
using the Nbac abstract <strong>model</strong>. We were skeptical that it was the abstraction<br />
technique that affected the verification results. Therefore, we made an<br />
equivalent Uppaal directly from PMC <strong>model</strong> since it was probably that the<br />
transformation from PMC <strong>model</strong> to Nbac <strong>model</strong> had some unfilled gaps. This<br />
Uppaal <strong>model</strong> is saved in file burn.xml. Again, Uppaal did prove the property<br />
for the same <strong>model</strong> with PMC. However, it is not our goal to see what<br />
was wrong with the <strong>model</strong> checkers so we did not go further into this issue.<br />
Since Uppaal could give a conclusive result for the algorithm, we had a<br />
chance to test the <strong>efficiency</strong> <strong>of</strong> verification on several abstract <strong>model</strong>s <strong>of</strong> this<br />
algorithm. However, we found that the difference <strong>of</strong> time and memory usage<br />
between different abstract <strong>model</strong>s was insignificant. The difference is mainly<br />
due to the difference in the physical size <strong>of</strong> the <strong>model</strong>. We believe that this<br />
system is too simple for the verification results on different abstract <strong>model</strong>s<br />
to be distinguishable. Table 5.1 presents some measurement data for this<br />
test.<br />
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