Section: New Results

Component-Based Architectures for On-the-Fly Verification

• EXP.OPEN now has two new options “-prob ” and “-rate ” for handling probabilistic and stochastic transitions, respectively; without these options, probabilistic and stochastic transitions are considered as ordinary transitions (this enables EXP.OPEN to be used for implementing alternative semantics, such as Interactive Probabilistic Chains  [27] where probabilistic transitions are synchronized using a global clock). Consequently, the former “-ratebranching ” option has been replaced by “-rate -branching ”.

  Also, error messages about synchronization vectors have been made more precise and EXP.OPEN performs tighter checks about labels containing only blanks and unexpected synchronization of probabilistic or stochastic transitions. Two bugs have been fixed in EXP.OPEN and style files have been added to bring support for the EXP format by mainstream text editors.

• A new option “-v ” has been added to set SVL variables from the command line (similar to “awk” or “make”). Debugging SVL scripts has been made easier: the “-debug ” option of SVL now stops the execution as soon as a shell command (e.g., a CADP tool or a Unix command) terminates with a non-zero exit status, so that problems are detected as soon as they occur.

  Also, SVL now performs tighter semantic checks, making sure that all partial-order reduction options passed to EXP.OPEN (namely, options explicitly set by the user and options automatically computed by SVL from the context of the EXP composition expression) are not contradictory.

• We developed the prototype tool TESTOR to extract test cases completely on the fly. Compared to TGV, the new tool TESTOR presents several advantages: (i) it has a more modular architecture, based on generic graph transformation components taken from the OPEN/CAESAR libraries ($\tau$-compression, $\tau$-confluence, $\tau$-closure, determinization, resolution of Boolean equation systems); (ii) it is capable of extracting a test case completely on the fly, by exploiting the diagnostic generation features of the Boolean equation system resolution algorithms; (iii) it enables a more flexible expression of test purposes, taking advantage of the multiway rendezvous, a primitive to express communication and synchronization among a set of distributed processes [15]. We evaluated TESTOR on three published case studies and more than $10000$ examples taken from the non-regression test suites of CADP. A paper describing this work was accepted for publication in an international conference.

• We also revised TGV, which is now by default much less verbose and only displays the most important information, but the former behaviour can still be retained using option “-verbose ”. A new option “-monitor ” allows to follow in real time how the test case generation progresses. Many warning and error messages have been enhanced, various bugs (especially buffer overflows) have been fixed, and memory allocation results are now strictly controlled.

In collaboration with Soren Enevoldsen (Aalborg University, Denmark), we studied the applicability of CADP tools for analyzing concurrent systems described using weighted CCS (WCCS) [43], an extension of CCS with an action prefix operator carrying a weight represented as a natural number. We developed a prototype OPEN/CAESAR-compliant compiler for WCCS, which enables to produce, in conjunction with the GENERATOR tool of CADP, the corresponding LTS model in which transitions are labeled with actions and weights. For specifying temporal properties of WCCS systems, we developed a prototype MCL library defining the operators of weighted CTL (WCTL) [43] using MCL fixed point operators parameterized by natural numbers. This library, used in conjunction with the EVALUATOR tool, provides an on-the-fly model checker for WCTL equipped with diagnostic capabilities (counterexamples and witnesses).