Catálogo de publicaciones - libros

Often when modelling systems, physical constraints on the resources available are needed. For example, we might say that at most processes can access a particular resource at any moment or exactly participants are needed for an agreement. Such situations are concisely modelled where propositions are constrained such that at most , or exactly , can hold at any moment in time. This paper describes both the logical basis and a verification method for propositional linear time temporal logics which allow such constraints as input. The method incorporates ideas developed earlier for a resolution method for the temporal logic TLX and a tableaux-like procedure for PTL. The complexity of this procedure is discussed and case studies are examined. The logic itself represents a combination of standard temporal logic with classical constraints restricting the numbers of propositions that can be satisfied at any moment in time.

We investigate the extension of modal logics by bisimulation quantifiers and present a class of modal logics which is decidable when augmented with bisimulation quantifiers. These logics are refered to as the idempotent transduction logics and are defined using the programs of propositional dynamic logic including converse and tests. This is a nontrivial extension of the decidability of the positive idempotent transduction logics which do not use converse operators in the programs (French, 2006). This extension allows us to apply bisimulation quantifiers to, for example, logics of knowledge, logics of belief and tense logics. We show the idempotent transduction logics preserve the axioms of propositional quantification and are decidable. The definition of idempotent transduction logics allows us to apply these results to a number of combined modal logics with a variety of interactions between modalities.

It can be desirable to specify polices that require a system to achieve some outcome even if a certain number of failures occur. This paper proposes a logic, RoCTL*, which extends CTL* with operators from Deontic logic, and a novel operator referred to as “Robustly”. This novel operator acts as variety of path quantifier allowing us to consider paths which deviate from the desired behaviour of the system. Unlike most path quantifiers, the Robustly operator must be evaluated over a path rather than just a state; the Robustly operator quantifies over paths produced from the current path by altering a single step. The Robustly operator roughly represents the phrase “even if an additional failure occurs now or in the future”. This paper examines the expressivity of this new logic, motivates its use and shows that it is decidable.

In abstract algebra, a structure is said to be Noetherian if it does not admit infinite strictly ascending chains of congruences. In this paper, we adapt this notion to first-order logic by defining the class of Noetherian theories. Examples of theories in this class are Linear Arithmetics without ordering and the empty theory containing only a unary function symbol. Interestingly, it is possible to design a non-disjoint combination method for extensions of Noetherian theories. We investigate sufficient conditions for adding a temporal dimension to such theories in such a way that the decidability of the satisfiability problem for the quantifier-free fragment of the resulting temporal logic is guaranteed. This problem is firstly investigated for the case of Linear time Temporal Logic and then generalized to arbitrary modal/temporal logics whose propositional relativized satisfiability problem is decidable.

We propose a new class of tree automata, called (TAN). This framework is obtained by extending equational tree automata, and improves the results of the previous work, such as: recognized tree languages modulo the (,) =  are closed under complement, which are closed in equational tree automata, besides we do not lose important decidability. In the paper, first we investigate the closure properties of this class for Boolean operations and the decidability relative to the equational tree automata. Next we consider the relationship to other automata frameworks, in particular, , which is a class of unranked tree automata. Hedge automata have been recognized in the XML database community as a theoretical basis for modeling the manipulation of semi-structured data. Through the observation about transformations from hedge automata to tree automata, we discuss advantages in the expressiveness and complexity of TAN. As an application of our framework, we show an example that XML schema with constraints that can not be dealt with by other tree automata frameworks is manipulated by TAN.

Constraint solvers are key modules in many systems with reasoning capabilities (e.g., automated theorem provers). To incorporate constraint solvers in such systems, the capability of producing conflict sets or explanations of their results is crucial. For expressiveness, constraints are usually built out in unions of theories and constraint solvers in such unions are obtained by modularly combining solvers for the component theories. In this paper, we consider the problem of modularly constructing conflict sets for a combined theory by re-using available proof-producing procedures for the component theories. The key idea of our solution to this problem is the concept of explanation graph, which is a labelled, acyclic and undirected graph capable of recording the entailment of some equalities. Explanation graphs allow us to record explanations computed by a proof-producing procedure and to refine the Nelson-Oppen combination method to modularly build conflict sets for disjoint unions of theories. We also study how the computed conflict sets relate to an appropriate notion of minimality.

To combine tree languages with term rewriting, we introduce a new class of tree languages, that both extends regular languages and restricts context-free languages, and that is closed under intersection (unlike context-free languages). To do it, we combine the concept of visibly pushdown language, with top-down pushdown tree automata, and we get the visibly pushdown tree automata. Then, we use them to express the sets of descendants for a sub-class of growing term rewrite systems, and thanks to closure under intersection, we get that joinability and (restricted) unifiability are decidable.

We introduce a propositional encoding of the recursive path order with status (RPO). RPO is a combination of a multiset path order and a lexicographic path order which considers permutations of the arguments in the lexicographic comparison. Our encoding allows us to apply SAT solvers in order to determine whether a given term rewrite system is RPO-terminating. Furthermore, to apply RPO within the dependency pair framework, we combined our novel encoding for RPO with an existing encoding for argument filters. We implemented our contributions in the termination prover AProVE. Our experiments show that due to our encoding, combining termination provers with SAT solvers improves the performance of RPO-implementations by orders of magnitude.