Matthew Parkinson Richard Bornat Cristiano Calcagno 9 DTR06-1.pdf

Hoare logic is bedevilled by complex and unmemorable side conditions on the use of variables. We define a logic free of side conditions, and show that it admits translations of proofs in Hoare logic, thereby showing that nothing is lost. Our work draws on ideas from separation logic: program variables are treated as resource and separated with *, rather than as logical variables in disguise. For clarity we exclude a treatment of the heap.

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Emmanuel Letier Jeff Kramer Jeff Magee Sebastian Uchitel 10 DTR06-2.pdf

Goal-oriented methods are increasingly popular for elaborating software requirements. They offer systematic support for incrementally building intentional, structural, and operational models of the software and its environment. Event-based transition systems on the other hand are convenient formalisms for modelling and reasoning about software behaviours at the architectural level. The paper combines these two works by presenting a technique .for translating formal specification of software operations built according to the KAOS goal-oriented method into event-based transition systems analysable by the LTSA toolset. The translation involves moving from a declarative, state-based, timed, synchronous formalism typical of requirements modelling languages to an operational, event-based, untimed, asynchronous one typical of architecture description languages. The derived model is used for the formal analysis and animation of KAOS operation models In LTSA. The translation process provides insights into the two complementary formalisms and raises questions about the use o f synchronous temporal logic for requirements specification.

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Krysia Broda Christopher J. Hogger 39 DTR06-3.pdf

A policy for a minimal reactive agent is a set of condition-action rules used to determine its response to perceived environmental stimuli. When the policy pre-disposes the agent to achieving a stipulated goal we call it a teleo-reactive policy. This paper presents a framework for constructing and evaluating teleo-reactive policies for one or more minimal agents, based upon discounted-reward evaluation of policy-restricted subgraphs of complete situation-graphs. The main feature of the method is that it exploits explicit and definite associations of the agent's perceptions with states. The combinatorial burden that would potentially ensue from such associations can be ameliorated by suitable use of abstractions. The framework allows one to plan for a number of agents by focusing upon the behaviour of a single representative of them. It allows for varied behaviour to be modelled, including communication between agents. Simulation results presented here indicate that the method affords a good degree of scalability and predictive power.

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Krysia Broda Christopher J. Hogger 12 DTR06-4.pdf

Abstraction is a valuable tool for dealing with scalability in large state space contexts. This paper addresses the design, using abstraction, of good policies for minimal autonomous agents applied within a situation-graph-framework. In this framework an agent's policy is some function that maps perceptual inputs to actions deterministically. A good policy disposes the agent towards achieving one or more designated goal situations, and the design process aims to identify such policies. The agents to which the framework applies are assumed to have only partial observability, and in particular may not be able to perceive fully a goal situation. A further assumption is that the environment may influence an agent's situation by unpredictable exogenous events, so that a policy cannot take advantage, of a reliable history of previous actions. The Bellman discount measure provides a means of evaluating situations and hence the overall value of a policy. When abstraction is used, the accuracy of the method can be significantly improved by modifying the standard Bellman equations. This paper describes the modification and demonstrates its power through comparison with simulation results.

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Alexander Artikis Marek Sergot Jeremy Pitt 39 DTR06-5.pdf

Electronic markets, dispute resolution and negotiation protocols are three types of application domains that can be viewed as open agent societies. Key characteristics of such societies are agent heterogeneity, conflicting individual goals and unpredictable behaviour. Members of such societies may fail to, or even choose not to, conform to the norms governing their interactions. It has been argued that systems of this type should have a formal, declarative, verifiable, and meaningful semantics. We present a theoretical and computational framework being developed for the executable specification of open agent societies. We adopt an external perspective and view societies as instances of normative systems. In this paper we demonstrate how the framework can be applied to specifying and executing a contract-net protocol. The specification is formalised in two action languages, the C+ language and the Event Calculus, and executed using respective software implementations, the Causal Calculator and the Society Visualiser. We evaluate our executable specification in the light of the presented case study, discussing the strengths and weaknesses of the employed action languages for the specification of open agent societies.

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Istvan Maros circa 20

The paper performs a theoretical and computational analysis of a new dual simplex algorithm GDPO that is based on an ever changing piecewise linear phase-1 objective function. It concludes that GDPO is able to considerably outperform the traditional dual phase-1 methods. It also offers enhanced numerically stability and more effectiveness in coping with degeneracy. Tests on 48 real life problems indicate that the theoretically possible improvements are very likely to materialize in practice thus making this algorithm a prime candidate for inclusion in any modern simplex solver.

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