VARIABLES AS RESOURCE IN HOARE LOGICSMatthew ParkinsonRichard BornatCristiano Calcagno9
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.]]>DERIVING EVENT-BASED TRANSITION SYSTEMS FROM GOAL-ORIENTED REQUIREMENTS MODELSEmmanuel LetierJeff KramerJeff MageeSebastian Uchitel10
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.]]>DESIGNING EFFECTIVE POLICIES FOR MINIMAL AGENTSKrysia BrodaChristopher J. Hogger39
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.
]]>OPTIMIZING MINIMAL AGENTS THROUGH ABSTRACTIONKrysia BrodaChristopher J. Hogger12
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.
]]>SPECIFYING NORM-GOVERNED COMPUTATIONAL SOCIETIESAlexander ArtikisMarek SergotJeremy Pitt39
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.
]]>COMPUTATIONAL STUDY OF THE GDPO DUAL PHASE-1 ALGORITHMIstvan Maroscirca 20The 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.]]>TRACE MODELLING FOR ABDUCTION BASECALLINGDavid J Thornley10
DTR06-7.pdf
DNA sequencing using the fluoresence based Sanger method comprises
interpretation of a sequence of signal peaks of varying size whose
colour indicates the presence of a base. We have established that
the ability to predict the variations effectively makes available
novel error correction information which will improve sequencing
efficacy. Our experiments so far have used basic models of the
Sanger reaction chemistry and machine learning techniques. These
have enabled us to make base calls just using context information,
specfically ignoring the peak data at the base calling position.
The 80% success rate of our blind experiments is striking, and will
be improved by a more accurate model of trace behaviour. To this
end, and to integrate the information into mainstream basecalling,
we wish to develop an enzyme kinetics model susceptible to
calibration of its component rates such that trace data can be
accurately predicted. We describe DNA sequencing trace data,
outline the trace prediction problem requirements on the model, and
discuss model construction and calibration issues.]]>ANISOTROPIC MULTIDIMENSIONAL SAVITZKY GOLAY KERNELS FOR SMOOTHING, DIFFERENTIATION AND RECONSTRUCTIONDavid J Thornley12
DTR06-8.pdf
The archetypal Savitzky-Golay convolutional filter matches a
polynomial to even-spaced data and uses this to measure smoothed
derivatives. We synthesize a scheme in which heterogeneous,
anisotropic linearly separable basis functions combine to provide a
general smoothing, derivative measurement and reconsruction function
for point coulds in multiple dimensions using a linear
operator in the form of a convolution kernel. We use a matrix
pseudo inverse for examples, but note that QR factorization is more
stable when free weighting is introduced.]]>EFFICIENT RE-INDEXING OF AUTOMATICALLY ANNOTATED IMAGE COLLECTIONS USING KEYWORD COMBINATIONAlexei YavlinskyStefan Rüger15
DTR06-9.pdf
This report presents a framework for improving the image index obtained
by automated image annotation. Within this framework, the technique of
keyword combination is used for fast image re-indexing based on initial
automated annotations. It aims to tackle the challenges of limited
vocabulary size and low annotation accuracies resulting from differences
between training and test collections. It is useful for situations when
these two problems are not anticipated at the time of annotation. We
show that based on example images from the automatically annotated
collection, it is often possible to find multiple keyword queries that
can retrieve new image concepts which are not present in the training
vocabulary, and improve retrieval results of those that are already
present. We demonstrate that this can be done at a very small
computational cost and at an acceptable performance tradeoff, compared
to traditional annotation models. We present a simple, robust, and
computationally efficient approach for finding an appropriate set of
keywords for a given target concept. We report results on TRECVID 2005,
Getty Image Archive, and Web image datasets, the last two of which were
specifically constructed to support realistic retrieval scenarios.]]>PROCEEDINGS OF THE 13TH INTERNATIONAL WORKSHOP ON EXPRESSIVENESS IN CONCURRENCY (EXPRESS'06)Roberto AmadioIain Phillips?This is the preliminary version of the proceedings of the 13th
International Workshop on Expressiveness in Concurrency (Express'06),
held in Bonn on 26 August 2006. It contains abstracts for invited talks
by Robin Milner (joint with the Infinity and SOS workshops) and Hagen
Völzer, together with seven contributed papers by the following authors:
Diletta Cacciagrano, Flavio Corradini and Catuscia Palamidessi; Xu Wang
and Marta Kwiatkowska; Ahmed Bouajjani, Jan Strejcek and Tayssir Touili;
Vincent Danos, Jean Krivine and Pawel Sobocinski; Daniele Gorla; Lucy
Saunders-Evans and Glynn Winskel; Luís Caires and Hugo Torres Vieira.
The final version will appear in Electronic Notes in Theoretical
Computer Science.
]]>