Dario Della Monica

Decidable and Undecidable Fragments of Halpern and Shoham's Interval Temporal Logic: Towards a Complete Classification

Interval temporal logics are based on temporal structures where time intervals, rather than time instants, are the primitive ontological entities. They employ modal operators corresponding to various relations between intervals, known as Allens relations. Technically, validity in interval temporal logics translates to dyadic second-order logic, thus explaining their complex computational behavior. The full modal logic of Allens relations, called HS, has been proved to be undecidable by Halpern and Shoham under very weak assumptions on the class of interval structures, and this result was discouraging attempts for practical applications and further research in the field. A renewed interest has been recently stimulated by the discovery of interesting decidable fragments of HS. This paper contributes to the characterization of the boundary between decidability and undecidability of HS fragments. It summarizes known positive and negative results, it describes the main techniques applied so far in both directions, and it establishes a number of new undecidability results for relatively small fragments of HS.

The dark side of interval temporal logic: marking the undecidability border

Unlike the Moon, the dark side of interval temporal logics is the one we usually see: their ubiquitous undecidability. Identifying minimal undecidable interval logics is thus a natural and important issue in that research area. In this paper, we identify several new minimal undecidable logics amongst the fragments of Halpern and Shoham’s logic HS, including the logic of the overlaps relation, over the classes of all finite linear orders and all linear orders, as well as the logic of the meets and subinterval relations, over the classes of all and dense linear orders. Together with previous undecidability results, this work contributes to bringing the identification of the dark side of interval temporal logics very close to the definitive picture.

Expressiveness of the interval logics of Allen's relations on the class of all linear orders: complete classification

We compare the expressiveness of the fragments of Halpern and Shohams interval logic (HS), i.e., of all interval logics with modal operators associated with Allens relations between intervals in linear orders. We establish a complete set of inter-definability equations between these modal operators, and thus obtain a complete classification of the family of 212 fragments of HS with respect to their expressiveness. Using that result and a computer program, we have found that there are 1347 expressively different such interval logics over the class of all linear orders.

The Dark Side of Interval Temporal Logic: Sharpening the Undecidability Border

Unlike the Moon, the dark side of interval temporal logics is the one we usually see: their ubiquitous undesirability. Identifying minimal undecidable interval logics is thus a natural and important issue in the research agenda in the area. The decidability status of a logic often depends on the class of models (in our case, the class of interval structures)in which it is interpreted. In this paper, we have identified several new minimal undecidable logics amongst the fragments of Halpern-Shoham logic HS, including the logic of the overlaps relation, over the classes of all and finite linear orders, as well as the logic of the meet and subinterval relations, over the class of dense linear orders. Together with previous undecid ability results, this work contributes to delineate the border of the dark side of interval temporal logics quite sharply.

On a Logic for Coalitional Games with Priced-Resource Agents

Alternating-time Temporal Logic (ATL) and Coalition Logic (CL) are well-established logical formalisms particularly suitable to model games between dynamic coalitions of agents (like e.g. the system and the environment). Recently, the ATL formalism has been extended in order to take into account boundedness of the resources needed for a task to be performed. The resulting logic, called Resource-BoundedATL (RB-ATL), has been presented in quite a variety of scenarios. Even if the model checking problem for extensions of ATL dealing with resource bounds is usually undecidable, a model checking procedure for RB-ATL has been proposed. In this paper, we introduce a new formalism, called PRB-ATL, based on a different notion of resource bounds and we show that its model checking problem remains in EXPTIME and has a PSPACE lower bound. Then, we tackle the problem of coalition formation. How and why agents should aggregate is not a new issue and has been deeply investigated, in past and recent years, in various frameworks, as for example in algorithmic game theory, argumentation settings, and logic-based knowledge representation. We face this problem in the setting of priced resource-bounded agents with the goal specified by an ATL formula. In particular we solve the problem of determining the minimal cost coalitions of agents acting in accordance to rules expressed by a priced game arena and satisfying a given formula. We show that such problem is computationally not harder than verifying the satisfaction of the same formula with fixed coalitions.

Metric propositional neighborhood logics on natural numbers

Interval logics formalize temporal reasoning on interval structures over linearly (or partially) ordered domains, where time intervals are the primitive ontological entities and truth of formulae is defined relative to time intervals, rather than time points. In this paper, we introduce and study Metric Propositional Neighborhood Logic (MPNL) over natural numbers. MPNL features two modalities referring, respectively, to an interval that is “met by” the current one and to an interval that “meets” the current one, plus an infinite set of length constraints, regarded as atomic propositions, to constrain the length of intervals. We argue that MPNL can be successfully used in different areas of computer science to combine qualitative and quantitative interval temporal reasoning, thus providing a viable alternative to well-established logical frameworks such as Duration Calculus. We show that MPNL is decidable in double exponential time and expressively complete with respect to a well-defined sub-fragment of the two-variable fragment

Undecidability of Interval Temporal Logics with the Overlap Modality

{{\rm FO}^2[\mathbb{N},=,<,s]}

Model checking coalitional games in shortage resource scenarios

of first-order logic for linear orders with successor function, interpreted over natural numbers. Moreover, we show that MPNL can be extended in a natural way to cover full