A Formal Approach to Agent Design: An Overview of Constraint-Based Agents

Formal models for agent design are important for both practical and theoretical reasons. The Constraint-Based Agent (CBA) design approach includes two formal models: Constraint Nets and Timed -automata. A constraint net models the agents and the environment symmetrically as, possibly hybrid, dynamical systems; a timed -automaton specifies the desired real-time dynamic behaviors of the situated agents. Given a constraint-based specification of the desired behavior, a constraint-based agent can be synthesized as a constraint solver. Using formal modeling and specification, it is also possible to verify complex agents as obeying real-time temporal constraint specifications. This overview paper presents a summary of the development and application of the CBA framework.     

A graph-theoretic optimal control problem for terminating discrete event processes

Most of the results to date in discrete event supervisory control assume a zero-or-infinity structure for the cost of controlling a discrete event system, in the sense that it costs nothing to disable controllable events while uncontrollable events cannot be disabled (i.e., their disablement entails infinite cost). In several applications however, a more refined structure of the control cost becomes necessary in order to quantify the tradeoffs between candidate supervisors. In this paper, we formulate and solve a new optimal control problem for a class of discrete event systems. We assume that the system can be modeled as a finite acylic directed graph, i.e., the system process has a finite set of event trajectories and thus is terminating. The optimal control problem explicitly considers the cost of control in the objective function. In general terms, this problem involves a tradeoff between the cost of system evolution, which is quantified in terms of a path cost on the event trajectories generated by the system, and the cost of impacting on the external environment, which is quantified as a dynamic cost on control. We also seek a least restrictive solution. An algorithm based on dynamic programming is developed for the solution of this problem. This algorithm is based on a graph-theoretic formulation of the problem. The use of dynamic programming allows for the efficient construction of an optimal subgraph (i.e., optimal supervisor) of the given graph (i.e., discrete event system) with respect to the cost structure imposed. We show that this algorithm is of polynomial complexity in the number of vertices of the graph of the system.Research supported in part by the National Science Foundation under grant ECS-9057967 with additional support from GE and DEC.     

Robot Dynamic Modeling Using a Power Flow Approach with Application to Biped Locomotion

In this paper, we present a method for robots modeling called bidirectional dynamic modeling. This new method takes into account the gear efficiency and the direction of power transmission in the gears. Epicyclic gearboxes have often different efficiencies in the two directions of power transmission. The characteristics of the chain of transmission must then be taken into consideration in order to describe the dynamic behavior of robots. The two directions of power flow can indeed occur in robot motions. Depending on that direction the dynamic model is different. The bidirectional dynamic modeling is experimentally applied to a bipedal walking robot. Our method exhibits a better accuracy over classical modeling. Moreover, when applied to computed torque control, the bidirectional model increases the tracking performances.     

Robotic Tasks Using Path Control: Two Case Studies

Some robotic tasks usually achieved through motion control – trajectory tracking control – can be also well performed by resorting to path control philosophy. This is the case for applications where motion coordination among the robot joints is more important than joint tracking of a timed desired reference. This paper illustrates this concept by means of two academic case studies – theory and experiments – using a two degrees-of-freedom direct-drive revolute arm.     

Modular visions: Referents, context and strategies for database open media works

The processes of constructing meaning in digital database environments entail a paradigm shift from previous models of audio-visual communication. Media emerging from the Electro-mechanical era (film/TV/video) present fixed spatio-temporal linearity and material conditions which objectify and render passive viewer and process. The problematic aspects of cinematic communication were addressed by Latin American filmmakers of the Third Cinema movement. Their concerns and approach presaged and assisted an understanding of the radical redefinition of audio-visual communication possible with digital databases. The conceptual and aesthetic aspirations of Third Cinema artists such as Julio Garcia Espinosa and Fernando Solanas were ultimately contradictory to linear media and find their fitting medium in digital modular construction. The materiality of database expression lacks an intrinsic temporal or spatial state and permits a more dynamic and multidirectional set of power relationships between author/s, piece, viewer/s. Other important referents for contextualising database art are modern art practitioners that rejected linear representational space and fractured the centrality of authorship. The author's own work, ...two, three, many Guevaras, an exploratory database environment, embraces the redefinition of process as artistic expression, the empowerment of interacting generative forces, and serves to illustrate the revolutionary potential of the new media.     

Development of an autonomous underwater robot “Twin-Burger” for testing intelligent behaviors in realistic environments

An autonomous underwater robot named Twin-Burger was developed as a versatile test bed to establish the techniques which realize intelligent robot behaviors. The robot was designed to have necessary functions for complex tasks including cooperative task execution with other robots and divers. The first robot Twin-Burger I was completed and launched in November 1992. This paper describes hardware and software systems of the robot. Motion of the robot is controlled by sliding controllers based on simplified equations of motion which are derived from system identification experiments. Tank tests proved that the robot was able to cruise along a commanded path as a sequence of control actions generated by the sliding controllers. The Distributed Vehicle Management Architecture (DVMA) is applied to the robot as an architecture for the control software. Mission execution experiments shows that the Twin-Burger behaves appropriately according to the mission and environmental conditions.     

A Typology of Translation Problems for Eurotra Translation Machines

This paper presents a detailed study of Eurotra Machine Translation engines, namely the mainstream Eurotra software known as the E-Framework, and two unofficial spin-offs – the C,A,T and Relaxed Compositionality translator notations – with regard to how these systems handle hard cases, and in particular their ability to handle combinations of such problems. In the C,A,T translator notation, some cases of complex transfer are wild, meaning roughly that they interact badly when presented with other complex cases in the same sentence. The effect of this is that each combination of a wild case and another complex case needs ad hoc treatment. The E-Framework is the same as the C,A,T notation in this respect. In general, the E-Framework is equivalent to the C,A,T notation for the task of transfer. The Relaxed Compositionality translator notation is able to handle each wild case (bar one exception) with a single rule even where it appears in the same sentence as other complex cases.     

The multi-dimensional concordance: A new tool for literary research

This paper describes the use of correspondence analysis to create the space of a book, constructs that of Kierkegaard'sFear and Trembling as an illustration, and distinguishes three separate contexts of some of its most important words: thespatial context (where the search word lies in that named and ordered space); theoverall context (the x words closest to the search word in multi-dimensional space); and the role/sense context (the words associated with the search word in each of its most important roles, some of which may represent new senses.) It describes the identification of these contexts, discusses their importance and concludes by noting certain respects in which the procedure might perhaps be improved. Alastair McKinnon is Professor Emeritus of McGill's Department of Philosophy and has just been appointed research consultant at the new Kierkegaard Research Center in Copenhagen. His most recent publications include electronic versions of Wittgenstein's Published Writingsand Kierkegaard's Dagbøger.     

The Wave & Probe Communication Mechanisms

This paper is motivated by the modifications recently suggested to enhance TCP performance over wireless channels. We argue that TCP end-to-end error-control mechanism lacks the functionality to respond appropriately in situations where errors vary in nature, frequency, or duration. As a result, this mechanism could, under some circumstances, yield zero throughput achievements at high energy-cost, or degrade throughput performance without conserving energy. This incompetent behavior with respect to the energy/throughput tradeoff puts in question TCP's suitability as a universal, reliable transport protocol of choice, especially for battery-powered mobile devices for which energy is a critical resource and congestion is not the exclusive cause of errors.We propose Wave and Probing communication and control mechanisms that permit end-to-end protocols to detect congestion without necessarily experiencing packet drops, to distinguish random and burst errors from congestion, and, as conditions vary, to rapidly adjust the transmission window upwards or downwards depending on the nature of the error. We report extensively on the performance of these new mechanisms to demonstrate their energy-conserving and high-throughput capabilities.     

Distributed Control for 3D Metamorphosis

In this paper, we define Proteo as a class of three-dimensional (3D) metamorphic robotic system capable of approximating arbitrary 3D shapes by utilizing repeated modules. Each Proteo module contains embedded sensors, actuators and a controller, and each resides in a 3D grid space. A module can move itself to one of its open neighbor sites under certain motion constraints. Distributed control for the self-reconfiguration of such robots is an interesting and challenging problem. We present a class of distributed control algorithms for the reconfiguration of Proteo robots based on the goal-ordering mechanism. Performance results are shown for experiments of these algorithms in a simulation environment, and the properties of these algorithms are analyzed.     

A Philosophical Approach to the Concept of Data Model: Is a Data Model, in Fact, a Model?

The design of the database is crucial to the process of designing almost any Information System (IS) and involves two clearly identifiable key concepts: schema and data model, the latter allowing us to define the former. Nevertheless, the term model is commonly applied indistinctly to both, the confusion arising from the fact that in Software Engineering (SE), unlike in formal or empirical sciences, the notion of model has a double meaning of which we are not always aware. If we take our idea of model directly from empirical sciences, then the schema of a database would actually be a model, whereas the data model would be a set of tools allowing us to define such a schema.The present paper discusses the meaning of model in the area of Software Engineering from a philosophical point of view, an important topic for the confusion arising directly affects other debates where model is a key concept. We would also suggest that the need for a philosophical discussion on the concept of data model is a further argument in favour of institutionalizing a new area of knowledge, which could be called: Philosophy of Engineering.     

Concurrent processing in nonlinear column stability

A concurrent processing algorithm is developed for materially nonlinear stability analysis of imperfect columns with biaxial partial rotational end restraints. The algorithm for solving the governing nonlinear ordinary differential equations is implemented on a multiprocessor computer called the finite element machine, developed at the NASA Langley Research Center. Numerical results are obtained on up to nine concurrent processors. A substantial computational gain is achieved in using the parallel processing approach.     

Pheromone Robotics

We describe techniques for coordinating the actions of large numbers of small-scale robots to achieve useful large-scale results in surveillance, reconnaissance, hazard detection, and path finding. We exploit the biologically inspired notion of a virtual pheromone, implemented using simple transceivers mounted atop each robot. Unlike the chemical markers used by insect colonies for communication and coordination, our virtual pheromones are symbolic messages tied to the robots themselves rather than to fixed locations in the environment. This enables our robot collective to become a distributed computing mesh embedded within the environment, while simultaneously acting as a physical embodiment of the user interface. This leads to notions of world-embedded computation and world-embedded displays that provide different ways to think about robot colonies and the types of distributed computations that such colonies might perform.     

Fuzzy measurement in the Mishnah and the Talmud

I discuss the attitude of Jewish law sources from the 2nd–:5th centuries to the imprecision of measurement. I review a problem that the Talmud refers to, somewhat obscurely, as impossible reduction. This problem arises when a legal rule specifies an object by referring to a maximized (or minimized) measurement function, e.g., when a rule applies to the largest part of a divided whole, or to the first incidence that occurs, etc. A problem that is often mentioned is whether there might be hypothetical situations involving more than one maximal (or minimal) value of the relevant measurement and, given such situations, what is the pertinent legal rule. Presumption of simultaneous occurrences or equally measured values are also a source of embarrassment to modern legal systems, in situations exemplified in the paper, where law determines a preference based on measured values. I contend that the Talmudic sources discussing the problem of impossible reduction were guided by primitive insights compatible with fuzzy logic presentation of the inevitable uncertainty involved in measurement. I maintain that fuzzy models of data are compatible with a positivistic epistemology, which refuses to assume any precision in the extra-conscious world that may not be captured by observation and measurement. I therefore propose this view as the preferred interpretation of the Talmudic notion of impossible reduction. Attributing a fuzzy world view to the Talmudic authorities is meant not only to increase our understanding of the Talmud but, in so doing, also to demonstrate that fuzzy notions are entrenched in our practical reasoning. If Talmudic sages did indeed conceive the results of measurements in terms of fuzzy numbers, then equality between the results of measurements had to be more complicated than crisp equations. The problem of impossible reduction could lie in fuzzy sets with an empty core or whose membership functions were only partly congruent. Reduction is impossible may thus be reconstructed as there is no core to the intersection of two measures. I describe Dirichlet maps for fuzzy measurements of distance as a rough partition of the universe, where for any region A there may be a non-empty set of - _A (upper approximation minus lower approximation), where the problem of impossible reduction applies. This model may easily be combined with probabilistic extention. The possibility of adopting practical decision standards based on -cuts (and therefore applying interval analysis to fuzzy equations) is discussed in this context. I propose to characterize the uncertainty that was presumably capped by the old sages as U-uncertainty, defined, for a non-empty fuzzy set A on the set of real numbers, whose -cuts are intervals of real numbers, as U(A) = 1/h(A) ₀ ^h(A) log [1+(A)]d, where h(A) is the largest membership value obtained by any element of A and (A) is the measure of the -cut of A defined by the Lebesge integral of its characteristic function.     

Scene Determination Based on Video and Audio Features

Determining automatically what constitutes a scene in a video is a challenging task, particularly since there is no precise definition of the term scene. It is left to the individual to set attributes shared by consecutive shots which group them into scenes. Certain basic attributes such as dialogs, settings and continuing sounds are consistent indicators. We have therefore developed a scheme for identifying scenes which clusters shots according to detected dialogs, settings and similar audio. Results from experiments show automatic identification of these types of scenes to be reliable.     

On tolerable and desirable behaviors in supervisory control of discrete event systems

We formulate and solve a new supervisory control problem for discrete event systems. The objective is to design a logical controller—or supervisor—such that the discrete event system satisfies a given set of requirements that involve event ordering. The controller must deal with a limited amount of controllability in the form of uncontrollable events. Our problem formulation considers that the requirements for the behavior (i.e., set of traces) of the controlled system are specified in terms of a desired behavior and a larger tolerated behavior. Due to the uncontrollable events, one may wish to tolerate behavior that sometimes exceeds the ideal desired behavior if overall this results in achieving more of the desired behavior. The general solution of our problem is completely characterized. The nonblocking solution is also analyzed in detail. This solution requires the study of a new class of controllable languages. Several results are proved about this class of languages. Algorithms to compute certain languages of interest within this class are also presented.Research supported in part by the National Science Foundation under grants ECS-8707671, ECS-9057967, and ECS-9008947.     

The ethics of NHS computing: A terminal case

Value in the British National Health Service have shifted away from patient care towards financial control. However, in the quest for efficiency, huge amounts of NHS money have been wasted on computer system which failed. In this paper, I draw on a case study to explore some of the ethical issues which underlie this kind of waste of resources. Issues include the gap between public pronouncements and personal experience, the chaos of which lies behind the facade of rationality, and the systematic silencing of people, usually women, who question the viability of computer systems which are created for private gain rather than public service.     

Methods for the Reduction of Odometry Errors in Over-Constrained Mobile Robots

This paper presents an analysis of odometry errors in over-constrained mobile robots, that is, vehicles that have more independent motors than degrees of freedom. Examples of over-constrained vehicles are the various 6-wheeled Mars Rovers like Rocky-7, Rocky-8, or Fido.Based on our analysis we developed two novel measures aimed at reducing odometry errors. We also developed a novel method that serves as a framework for the implementation of the two new measures, as well as for other, conventional error reducing measures.One of the two new measures, called Fewest Pulses Measure, makes use of the observation that most terrain irregularities, as well as wheel slip, result in an erroneous overcount of encoder pulses. The second new measure, called Cross-coupled Control Measure, optimizes the motor control algorithm of the robot to reduce synchronization errors that would otherwise result in wheel slip with conventional controllers.The novel method that serves as a framework for other measures is based on so-called Expert Rules. In this paper we formulate three expert rules aimed at reducing dead-reckoning errors. Two of these expert rules are related to the foregoing discussion on error reducing measures. The third expert rule adds a gyroscope to the system and we re-examine the effectiveness of the odometry error-reducing measures in the context of this addition.In the work described in this paper we modified a Pioneer AT skid-steer platform by providing it with four independent drive motors and encoders. We implemented our error-reducing measures and the expert rule method on this over-constrained platform and present experimental results.     

Linear Interval Tolerance Problem and Linear Programming Techniques

In this paper, we consider the linear interval tolerance problem, which consists of finding the largest interval vector included in ([A], [b]) = {x R ⁿ | A [A], b [b], Ax = b}. We describe two different polyhedrons that represent subsets of all possible interval vectors in ([A], [b]), and we provide a new definition of the optimality of an interval vector included in ([A], [b]). Finally, we show how the Simplex algorithm can be applied to find an optimal interval vector in ([A], [b]).