Reasoning About Systems with Transition Fairness

Abstract. Formal verification methods model systems by Kripke structures. In order to model live behaviors of systems, Kripke structures are augmented with fairness conditions. Such conditions partition the computations of the systems into fair computations, with respect to which verification proceeds, and unfair computations, which are ignored. Reasoning about Kripke structures augmented with fairness is typically harder than reasoning about non-fair Kripke structures. We consider the transition fairness condition, where a computation π is fair iff each transition that is enabled in π infinitely often is also taken in π infinitely often. Transition fairness is a natural and useful fairness condition. We show that reasoning about Kripke structures augmented with transition fairness is not harder than reasoning about non-fair Kripke structures. We demonstrate it for fair CTL and LTL model checking, and the problem of calculating the dominators and postdominators.

Experimental Analysis of Different Techniques for Bounded Model Checking

Abstract. Bounded model checking (BMC) is a procedure that searches for counterexamples to a given property through bounded executions of a non-terminating system. This paper compares the performance of SAT-based, BDD-based and explicit state based BMC on benchmarks drawn from commercial designs. Our experimental framework provides a uniform and comprehensive basis to evaluate each of these approaches. The experimental results in this paper suggest that for designs with deep counterexamples, BDD-based BMC is much faster. For designs with shallow counterexamples, we observe that indeed SAT-based BMC is more effective than BDD-based BMC, but we also observe that explicit state based BMC is comparably effective, a new observation.

Symbolic Model Checking With Fewer Fixpoint Computations

Symbolic model checking, smc, is a decision procedure that verifies that some finite-state structure is a model for a formula of Computation Tree Logic (CTL). smc is based on fixpoint computations. Unfortunately, as the size of a structure grows exponentially with the number of state components, smc is not always powerful enough to handle realistic problems. We first show that a subset of CTL formulas can be checked by testing simple sufficient conditions, that do not require any fixpoint computation. Based on these observations, we identify a second, larger, subset of CTL that can by verified with fewer fixpoint computations than smc. We propose a model checking algorithm for CTL that tests the identified sufficient conditions whenever possible and falls back to smc otherwise. In the best (resp. worst) case, the complexity of this algorithm is exponentially better (resp. the same) in terms of state components than that of smc

Cancer Patient Disclosure and Patient-Doctor Communication of Complementary and Alternative Medicine Use: A Systematic Review

Objective. To explore the nondisclosure of complementary and alternative medicine (CAM) use among cancer patients, including reasons for and outcomes from nondisclosure of CAM use, within the context of patient-doctor communication. Method. A systematic review was conducted exploring investigations surrounding the communication of CAM use for patients with cancer published until August 2011. Results. A total of 21 studies were located, which reported a prevalence of CAM use among patients with cancer ranging between 11% and 95%; of these patients, 20% to 77% did not disclose their CAM use. The main reasons for nondisclosure were the doctor's lack of inquiry; patient's anticipation of the doctor's disapproval, disinterest, or inability to help; and patient's perception that disclosure of CAM use is irrelevant to their conventional care. There is some evidence to suggest that patient-doctor communication about the use of CAM was associated with an enhanced patient-doctor relationship and higher patient satisfaction. Conclusions. Although the use of CAM by patients with cancer is high, patients frequently fail to disclose its use to their health professionals for reasons emanating from both sides of the dyadic patient-doctor relationship. Because a substantial proportion of patients with cancer may use CAM and there is potential for herb- or vitamin-drug interactions, further research in patient-doctor communication about CAM is necessary to maintain patient safety and wellbeing. The development of effective interventions to improve the disclosure of CAM use should be an integral part of this future research

Model Checking Probabilistic Distributed Systems

Protocols for distributed systems make often use of random transitions to achieve a common goal. A popular example are randomized leader election protocols. We introduce probabilistic product automata (PPA) as a natural model for this kind of systems. To reason about these systems, we propose to use a product version of linear temporal logic (LTL# ). The main result of the paper is a model-checking procedure for PPA and LTL# . With its help, it is possible to check qualitative properties of distributed systems automatically