Annalisa Bossi

In this paper, we briefly describe our experience in the field of analysis and transformation of logic programs. Although now we work in completely different fields, verification of security properties on the one hand and biosystems analysis on the other, our previous experience continues to be a valuable guide.

We present a general unwinding framework for the definition of information flow security properties of concurrent programs, described in a simple imperative language enriched with parallelism and atomic statement constructors. We study different classes of programs obtained by instantiating the general framework and we prove that they entail the noninterference principle. Accurate proof techniques for the verification of such properties are defined by exploiting the Tarski decidability result for first-order formulae over the reals. Moreover, we illustrate how the unwinding framework can be instantiated in order to deal with intentional information release and we extend our verification techniques to the analysis of security properties of programs admitting downgrading.

We study the properties of input-consuming derivations of moded logic programs. Input-consuming derivations can be used to model the behavior of logic programs using dynamic scheduling and employing constructs such as delay declarations. We consider the class of nicely-moded programs and queries. We show that for these programs a weak version of the well-known switching lemma holds also for input-consuming derivations. Furthermore, we show that, under suitable conditions, there exists an algebraic characterization of termination of input-consuming derivations.

In logic programming, dynamic scheduling refers to a situation where the selection of the atom in each resolution (computation) step is determined at runtime, as opposed to a fixed selection rule such as the left-to-right one of Prolog. This has applications e.g. in parallel programming. A mechanism to control dynamic scheduling is provided in existing languages in the form of delay declarations. Input-consuming derivations were introduced to describe dynamic scheduling while abstracting from the technical details. In this paper, we first formalise the relationship between delay declarations and input-consuming derivations, showing in many cases a one-to-one correspondence. Then, we define a model-theoretic semantics for input-consuming derivations of simply-moded programs. Finally, for this class of programs, we provide a necessary and sufficient criterion for termination.