This technical note describes a monotone and continuous fixpoint operator to compute the answer sets of programs with aggregates. The fixpoint operator relies on the notion of aggregate solution. Under certain conditions, this operator behaves identically to the three-valued immediate consequence operator Φ P for aggregate programs, independently proposed in (Pelov 2004; Pelov et al. 2004). Thi...

We prove that the model checking problem for the existential fragment of first order (FO) logic on partially ordered sets is fixedparameter tractable (FPT) with respect to the formula and the width of a poset (the maximum size of an antichain). While there is a long line of research into FO model checking on graphs, the study of this problem on posets has been initiated just recently by Bova, G...

A stochastic timed automaton is a purely stochastic process defined on a timed automaton, in which both delays and discrete choices are made randomly. We study the almost-sure model-checking problem for this model, that is, given a stochastic timed automaton A and a property φ, we want to decide whether A satisfies φ with probability 1. In this paper, we identify several classes of automata and...

This article aims at reformulating in more current terms Hoekstra and Mulder’s (1990) analysis of the Locative Inversion (LI) construction, illustrated in (2b) below. The new proposal is crucially based on the assumption that Small Clause (SC) predicates agree with their external argument in φ-features, which may be morphologically reflected, as in the case of adjectival agreement in the Italia...

In a previous paper, we presented a technique called finite trace covers, in which a program is represented by a set of partial orders. We also presented classes of reachability properties that could be checked in time that is polynomial in the size of the trace cover. A deficiency of this approach was that it did not reduce the complexity of checking properties that did not belong to an effici...

Trigger querying is the problem of finding, given a system M and an LTL formula φ, the set of scenarios that trigger φ in M ; that is, the language L of finite computations of M such that all infinite computations that have a prefix in L continue with a suffix that satisfies φ. For example, the trigger query M |=? 7→ F err asks for the set of scenarios after which err aught to eventually happen...

Model checking approaches can be divided into two broad categories: global approaches that determine the set of all states in a model M that satisfy a temporal logic formula Φ, and local approaches in which, given a state s in M , the procedure determines whether s satisfies Φ. When s is a term of a process language, the model-checking procedure can be executed “on-the-fly”, driven by the synta...

The Timed Concurrent Constrain programming (tccp in short) is a concurrent logic language obtained by extending the cc paradigm with the notion of time and a suitable mechanism to model time-outs and preemptions. Thanks to these features, tccp is a suitable language to model both concurrent and reactive systems. The existing formal techniques for the verification of tccp are based on model chec...

Partial Order Reduction (POR) techniques improve the basic model checking algorithm by reducing the numbers of states and transitions explored in verifying a property of the model. In the “ample set” POR framework for the verification of an LTL−X formula φ, one associates to each state s a subset Ts of the set of all transitions enabled at s. The approach requires that whenever Ts is a proper s...

The application of model-checking tools to complex systems involves a nontrivial step of modelling the system by a finite-state model and a translation of the desired properties into a formal specification. While a positive answer of the model checker guarantees that the model satisfies the specification, correctness of the modelling is not checked. Vacuity detection is a successful approach fo...