Isabel Navarrete

On point-duration networks for temporal reasoning

We present here a point-duration network formalism which extends the point algebra model to include additional variables that represent durations between points of time. Thereafter the new qualitative model is enlarged for allowing unary metric constraints on points and durations, subsuming in this way several point-based approaches to temporal reasoning. We deal with some reasoning tasks within the new models and we show that the main problem, deciding consistency, is NP-complete. However, tractable special cases are identified and we show efficient algorithms for checking consistency, finding a solution and obtaining the minimal network.

Spatial reasoning with rectangular cardinal relations

Qualitative spatial representation and reasoning plays a important role in various spatial applications. In this paper we introduce a new formalism, we name RCD calculus, for qualitative spatial reasoning with cardinal direction relations between regions of the plane approximated by rectangles. We believe this calculus leads to an attractive balance between efficiency, simplicity and expressive power, which makes it adequate for spatial applications. We define a constraint algebra and we identify a convex tractable subalgebra allowing efficient reasoning with definite and imprecise knowledge about spatial configurations specified by qualitative constraint networks. For such tractable fragment, we propose several polynomial algorithms based on constraint satisfaction to solve the consistency and minimality problems. Some of them rely on a translation of qualitative networks of the RCD calculus to qualitative networks of the Interval or Rectangle Algebra, and back. We show that the consistency problem for convex networks can also be solved inside the RCD calculus, by applying a suitable adaptation of the path-consistency algorithm. However, path consistency can not be applied to obtain the minimal network, contrary to what happens in the convex fragment of the Rectangle Algebra. Finally, we partially analyze the complexity of the consistency problem when adding non-convex relations, showing that it becomes NP-complete in the cases considered. This analysis may contribute to find a maximal tractable subclass of the RCD calculus and of the Rectangle Algebra, which remains an open problem.

An energy efficient middleware for an ad-hoc AAL wireless sensor network

DIA (Dispositivo Inteligente de Alarma, in Spanish) is an AAL (Ambient Assisted Living) system that allows to infer a potential dangerous action of an elderly person living alone at home. This inference is obtained by a specific sensorisation with sensor nodes (portables and fixes) and a reasoning layer embedded in a PC that learns of the users behaviour patterns and advices when actual one differs significantly of the normal patterns. In AAL systems, energy is a limited resource therefore sensor devices need to be properly managed to conserve energy. In this paper, we introduce the design and implementation of innovative and specific mechanisms at the sensory layer middleware which is capable of, first to discriminate spurious motion detections assuming that these signals do not resemble the patterns of real motion detections and, second to reduce the dynamics of messages by a sensor signal processing in order to compress the whole information in one single event. The middleware achieves power saving by modifying the raw information from sensors and adapting it to the predefined semantic of the reasoning layer. It manages the important task of data processing from sensors (raw information), and transfers the pre-processed information into the top layer of reasoning in a more energy efficient way. We also address the trade-off between reducing power consumption and reducing delay for incoming data. We present results from experiments using our implementation of these mechanisms at the middleware that comprises from node firmware to the PC driver. The number of messages of the proposed method with respect to the raw data is reduced by approximately 98.5%. The resources used in the PIR signal processing is reduced by approximately 85%. The resulting delay introduced is small (10-19s) but system dynamics is slow enough to avoid contextualisation errors or reduction of system performance. We consider these results as very satisfactory.

Efficient resolution mechanism for fuzzy temporal constraint logic

In this paper we describe a module, the temporal solving module (TSM), for answering queries sent to a data blackboard which must take into account fuzzy temporal constraints among blackboard variables. The TSM receives the queries written in an interaction language that is translated into a language of a reified many-sorted first-order logic, called fuzzy temporal constraint logic (FTCL). This logic has been formalized in previous works, together with a sound resolution principle for it. We justify the search strategy used in the implementation of the unit resolution. The main results achieved in this work are the simplification criteria and the heuristic evaluation function given for improving the search process to achieve the refutation. First, we use the fuzzy number ordering functions proposed by Marin et al. (1997) for obtaining a simplification of queries that imply an exhaustive search in the data blackboard. Secondly, in order to prune the tree, we use a function to check the possibility of obtaining a fuzzy temporal instant different to the empty set, in the unification of two imprecise temporal variables.

Modeling a risk detection system for elderly's home-care with a network of timed automata

We address the problem of modeling a risk detection system oriented to elderlys home-care, which may cause the generation of an alarm if there is evidence of a serious problem. We have chosen a network of timed automata as a suitable formalism to solve the problem in a simple and elegant fashion. Our model is capable of representing the subjects environment, modeling his behavior dynamics, detecting several types of abnormal behavior patterns, and deciding whether they have enough evidence of being dangerous to generate an alarm. In addition, the formalism allows concurrent activity monitoring in different rooms, what is useful to determine if the person is alone at home, in order to avoid the generation of false alarms when the elder is supposed to be already under human care. We have verified critical properties of the model by using a model-checking engine.

A new modal logic for reasoning about space: spatial propositional neighborhood logic

It is widely accepted that spatial reasoning plays a central role in artificial intelligence, for it has a wide variety of potential applications, e.g., in robotics, geographical information systems, and medical analysis and diagnosis. While spatial reasoning has been extensively studied at the algebraic level, modal logics for spatial reasoning have received less attention in the literature. In this paper we propose a new modal logic, called spatial propositional neighborhood logic (SpPNL for short) for spatial reasoning through directional relations. We study the expressive power of SpPNL, we show that it is able to express meaningful spatial statements, we prove a representation theorem for abstract spatial frames, and we devise a (non-terminating) sound and complete tableaux-based deduction system for it. Finally, we compare SpPNL with the well-known algebraic spatial reasoning system called rectangle algebra.

Using temporal logic for spatial reasoning: temporalized propositional neighborhood logic

In this paper we develop a new modal logic for spatial reasoning called Temporalized Propositional Neighborhood Logic, which is the result of the application of a known technique called temporalization to a known temporal logic for spatial reasoning (PNL). We will show that our logic is expressive enough to formalize interesting spatial statements and that it is decidable in NEXPTIME.

Deciding consistency of a point-duration network with metric constraints

We introduce a new model, MPDN, for quantitative temporal reasoning with points and durations, that supposes an extension of the TCSP formalism and previous point-duration network models. The problem of deciding consistency for a MPDN is shown to be NP-complete. So, we identify a tractable fragment, named simple MPDN, that subsumes the STP model and allows for duration reasoning. Necessary and sufficient conditions for deciding consistency of a simple MPDN are used to design an algorithm for consistency checking, whose time complexity is cubic in the number of variables. This is a significant improvement, not only in computational complexity but also in simplicity, over previous non-specific algorithms that can be applied to solve the consistency problem.

Efficient Spatial Reasoning with Rectangular Cardinal Relations and Metric Constraints

In many real-world applications of knowledge representation and reasoning formalisms, one needs to cope with a number of spatial aspects in an integrated and efficient way. In this paper, we focus our attention on the so-called Rectangular Cardinal Direction calculus for qualitative spatial reasoning on cardinal relations between rectangles whose sides are parallel to the axes of a fixed reference system. We show how to extend its convex tractable fragment with metric constraints preserving tractability. The resulting formalism makes it possible to efficiently reason about spatial knowledge specified by one qualitative constraint network and two metric networks (one for each spatial dimension). In particular, it allows one to represent definite or imprecise knowledge on directional relations between rectangles and to derive additional information about them, as well as to deal with metric constraints on the height/width of a rectangle or on the vertical/horizontal distance between the sides of two rectangles. We believe that the formalism features a good combination of simplicity, efficiency, and expressive power, making it adequate for spatial applications like, for instance, web-document query processing and automatic layout generation.