Filtering Algorithms for the NValue Constraint

The NValue constraint counts the number of different values assigned to a vector of variables. Propagating generalized arc consistency on this constraint is NP-hard. We show that computing even the lower bound on the number of values is NP-hard. We therefore study different approximation heuristics for this problem. We introduce three new methods for computing a lower bound on the number of values. The first two are based on the maximum independent set problem and are incomparable to a previous approach based on intervals. The last method is a linear relaxation of the problem. This gives a tighter lower bound than all other methods, but at a greater asymptotic cost.     

Issues in distributed timed model checking

In this work we present Zeus, a distributed timed model checker that evolves from the TCTL model checker Kronos [13] and that currently can handle backwards computation of reachability properties [2] over timed automata [3].Zeus was developed following a software architecture-centric approach. Its conceptual architecture was conceived to be sufficiently modular to house several features such as a priori graph partitioning, synchronous and asynchronous computation, communication piggybacking, delayed messaging, and dead-time utilization.Surprisingly enough, early experiments pinpointed the difficulties of getting speedups using asynchronous versions and showed interesting results on the synchronous counterpart, although being intuitively less attractive.     

Dealing with practical limitations of distributed timed model checking for timed automata

Two base algorithms are known for reachability verification over timed automata. They are called forward and backwards, and traverse the automata edges using either successors or predecessors. Both usually work with a data structure called Difference Bound Matrices (DBMs). Although forward is better suited for on-the-fly construction of the model, the one known as backwards provides the basis for the verification of arbitrary formulae of the TCTL logic, and more importantly, for controller synthesis. Zeus is a distributed model checker for timed automata that uses the backwards algorithm. It works assigning each automata location to only one processor. This design choice seems the only reasonable way to deal with some complex operations involving many DBMs in order to avoid huge overheads due to distribution. This article explores the limitations of Zeus-like approaches for the distribution of timed model checkers.Our findings justify why close-to-linear speedups are so difficult –and sometimes impossible– to achieve in the general case. Nevertheless, we present mechanisms based on the way model checking is usually applied. Among others, these include model-topology-aware partitioning and on-the-fly workload redistribution. Combined, they have a positive impact on the speedups obtained.

Design and Testing of a Robotic System for mr Image-guided Interventions

The effective integration of robotics together with magnetic resonance (mr) technology is expected to facilitate the real-time guidance of various diagnostic and therapeutic interventions. Specially designed robotic manipulators are required for this purpose, the development of which is a challenging task given the strong magnetic fields and the space limitations that characterize the mr scanning environment. A prototype mr-compatible manipulator is presented, designed to operate inside cylindrical mr scanners. It was developed for the study of minimally invasive diagnostic and therapeutic interventions in the abdominal and thoracic area with real-time mr image guidance. Initial tests were performed inside a high-field clinical mr scanner and included mr-compatibility tests and phantom studies on image-guided targeting.     

Aggregate features and A<Emphasis Type="SmallCaps">DA</Emphasis>B<Emphasis Type="SmallCaps">OOST</Emphasis> for music classification

We present an algorithm that predicts musical genre and artist from an audio waveform. Our method uses the ensemble learner ADABOOST to select from a set of audio features that have been extracted from segmented audio and then aggregated. Our classifier proved to be the most effective method for genre classification at the recent MIREX 2005 international contests in music information extraction, and the second-best method for recognizing artists. This paper describes our method in detail, from feature extraction to song classification, and presents an evaluation of our method on three genre databases and two artist-recognition databases. Furthermore, we present evidence collected from a variety of popular features and classifiers that the technique of classifying features aggregated over segments of audio is better than classifying either entire songs or individual short-timescale features. Editor: Gerhard Widmer     

Proving Arrow’s theorem by <Emphasis Type="SmallCaps">PROLOG</Emphasis>

This paper presented a simple PROLOG implementation for Arrow’s Social welfare function (SWF). Arrow (Social choice and individual values, Yale University Press, 1963) proved that any SWF which satisfies a set of conditions IIA, Pareto, and unrestricted domain should be dictatorial. The PROLOG program can prove the theorem for 3-alternative 2-agent case. With a minor modification it proves a version of the theorem without the Pareto condition by Wilson (Journal of Economic Theory, 5, 478–486, 1972).     

A General Framework for Combining Visual Trackers – The "Black Boxes" Approach

Over the past few years researchers have been investigating the enhancement of visual tracking performance by devising trackers that simultaneously make use of several different features. In this paper we investigate the combination of synchronous visual trackers that use different features while treating the trackers as “black boxes”. That is, instead of fusing the usage of the different types of data as has been performed in previous work, the combination here is allowed to use only the trackers' output estimates, which may be modified before their propagation to the next time step. We propose a probabilistic framework for combining multiple synchronous trackers, where each separate tracker outputs a probability density function of the tracked state, sequentially for each image. The trackers may output either an explicit probability density function, or a sample-set of it via Condensation. Unlike previous tracker combinations, the proposed framework is fairly general and allows the combination of any set of trackers of this kind, even in different state-spaces of different dimensionality, under a few reasonable assumptions. The combination may consist of different trackers that track a common object, as well as trackers that track separate, albeit related objects, thus improving the tracking performance of each object. The benefits of merely using the final estimates of the separate trackers in the combination are twofold. Firstly, the framework for the combination is fairly general and may be easily used from the software aspects. Secondly, the combination may be performed in a distributed setting, where each separate tracker runs on a different site and uses different data, while avoiding the need to share the data. The suggested framework was successfully tested using various state-spaces and datasets, demonstrating that fusing the trackers' final distribution estimates may indeed be applicable. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. First online version published in October, 2005     

Programming recursively defined functions infortran

Various approaches to the problem of programming recursively defined functions infortran are discussed. The only acceptable method in ASAfortran is shown to be most easily programmed using a stack containing not addresses, but function arguments. The stack is built up and, when full, the function is constructed from the stack elements. A sequence of examples of increasing complexity is given to demonstrate the technique, including one in which a queue is found to be more appropriate than a stack. The emphasis throughout is on the simplicity of the technique.     

Nivel: a metamodelling language with a formal semantics

Much work has been done to clarify the notion of metamodelling and new ideas, such as strict metamodelling, distinction between ontological and linguistic instantiation, unified modelling elements and deep instantiation, have been introduced. However, many of these ideas have not yet been fully developed and integrated into modelling languages with (concrete) syntax, rigorous semantics and tool support. Consequently, applying these ideas in practice and reasoning about their meaning is difficult, if not impossible. In this paper, we strive to add semantic rigour and conceptual clarity to metamodelling through the introduction of Nivel, a novel metamodelling language capable of expressing models spanning an arbitrary number of levels. Nivel is based on a core set of conceptual modelling concepts: class, generalisation, instantiation, attribute, value and association. Nivel adheres to a form of strict metamodelling and supports deep instantiation of classes, associations and attributes. A formal semantics is given for Nivel by translation to weight constraint rule language (WCRL), which enables decidable, automated reasoning about Nivel. The modelling facilities of Nivel and the utility of the formalisation are demonstrated in a case study on feature modelling.

Privacy-preserving boosting

We describe two algorithms, BiBoost (Bipartite Boosting) and MultBoost (Multiparty Boosting), that allow two or more participants to construct a boosting classifier without explicitly sharing their data sets. We analyze both the computational and the security aspects of the algorithms. The algorithms inherit the excellent generalization performance of AdaBoost. Experiments indicate that the algorithms are better than AdaBoost executed separately by the participants, and that, independently of the number of participants, they perform close to AdaBoost executed using the entire data set. Responsible Editor: Charu Aggarwal.     

Safe design of high-performance embedded systems in an MDE framework

In this paper, we use the UML MARTE profile to model high-performance embedded systems (HPES) in the GASPARD2 framework. We address the design correctness issue on the UML model by using the formal validation tools associated with synchronous languages, i.e., the SIGALI model checker, etc. This modeling and validation approach benefits from the advantages of UML as a standard, and from the number of validation tools built around synchronous languages. In our context, model transformations act as a bridge between UML and the chosen validation technologies. They are implemented according to a model-driven engineering approach. The modeling and validation are illustrated using the multimedia functionality of a new-generation cellular phone.     

A comparison of tools for teaching formal software verification

We compare four tools regarding their suitability for teaching formal software verification, namely the Frege Program Prover, the Key system, Perfect Developer, and the Prototype Verification System (PVS). We evaluate them on a suite of small programs, which are typical of courses dealing with Hoare-style verification, weakest preconditions, or dynamic logic. Finally we report our experiences with using Perfect Developer in class.     

Schedulability analysis of global edf

The multiprocessor edf scheduling of sporadic task systems is studied. A new sufficient schedulability test is presented and proved correct. It is shown that this test generalizes the previously-known exact uniprocessor edf-schedulability test, and that it offers non-trivial quantitative guarantees (including a resource augmentation bound) on multiprocessors.

A formal approach to reactive systems software: A telecommunications application in Esterel

Esterel is a formally-defined language designed for programming reactive systems; namely, those that maintain a permanent interaction with their environment. The AT&T 5ESS^® telephone switching system is an example of a reactive system. We describe an implementation in Esterel of one feature of a 5ESS switch; this implementation has been tested in the 5ESS switch simulator. Furthermore, it has been formally verified that this implementation satisfies some safety properties stated by 5ESS software development. Our experience indicates that Esterel is suitable for programming industrial-strength reactive systems, and affords significant advantages in software development over more traditional programming languages used in industrial settings.An earlier version of this paper appeared in the Proceedings of the Workshop on Industrial-Strength Formal Specification Techniques, Boca Raton, Florida, 1995.The author is currently supported by a Fulbright fellowship from Spain's Ministry of Science and Education. The work described here was performed while the author was visiting AT&T Bell Laboratories.     

Test generation for radiotherapy accelerators

System specification with Lotos (Language Of Temporal Ordering Specification) is briefly introduced. To make test generation practicable, specifications are annotated with event constraints using PCL (Parameter Constraint Language) as a means of stating test purposes. Automated test generation can then use the principle of input-output conformance to check whether an implementation agrees with its specification. Test suites are generated by a transition tour that either visits every transition at least once (for infinite behaviour) or follows every path (for finite behaviour). The approach is applied to a case study in which tests are generated for radiotherapy accelerators used in cancer treatment. A typical specification and set of test purposes yields 256 test cases that can be executed manually or automatically. The goal is to determine situations in which an accelerator does not behave in conformity with its specification.     

Inverse NP Problems

The inverse problem relative to a verifier V of proofs of membership for a NP language is the problem of deciding, given a set π of proofs, whether or not there exists a string x having exactly π as its set of proofs. In this paper, we study the complexity of inverse problems. We develop a new notion of reduction which allows one to compare the complexity of inverse problems. Using this notion, we classify as coNP-complete the inverse problems for the “natural” verifiers of many NP-complete problems. We also show that the inverse complexity of a verifier for a language L cannot be predicted solely from the complexity of L, but rather, is highly dependent upon the choice of verifier used to accept L. In this context, a verifier with a Σ₂ ^p -complete inverse problem is exhibited, giving a new and natural example of a Σ₂ ^p -complete problem.      

The KeY tool

KeY is a tool that provides facilities for formal specification and verification of programs within a commercial platform for UML based software development. Using the KeY tool, formal methods and object-oriented development techniques are applied in an integrated manner. Formal specification is performed using the Object Constraint Language (OCL), which is part of the UML standard. KeY provides support for the authoring and formal analysis of OCL constraints. The target language of KeY based development is Java Card DL, a proper subset of Java for smart card applications and embedded systems. KeY uses a dynamic logic for Java Card DL to express proof obligations, and provides a state-of-the-art theorem prover for interactive and automated verification. Apart from its integration into UML based software development, a characteristic feature of KeY is that formal specification and verification can be introduced incrementally.     

The Long-Term Forecast for Weather Bulletin Translation

Machine Translation (MT) is the focus of extensive scientific investigations driven by regular evaluation campaigns, but which are mostly oriented towards a somewhat particular task: translating news articles into English. In this paper, we investigate how well current MT approaches deal with a real-world task. We have rationally reconstructed one of the only MT systems in daily use which produces high-quality translation: the Météo system. We show how a combination of a sentence-based memory approach, a phrase-based statistical engine and a neural-network rescorer can give results comparable to those of the current system. We also explore another possible prospect for MT technology: the translation of weather alerts, which are currently being translated manually by translators at the Canadian Translation Bureau.     

Lexicons

The three lexicons used by KBMT-89 are described: A concept lexicon constitutes the sublanguage domain model for specifying semantic information; it is maintained by Ontos, a knowledge-acquisition and maintenance system. An analysis lexicon is a dictionary containing syntactic information and mapping rules required for semantic parsing. And a generation lexicon, similar to the analysis lexicon, is employed in the generation phase.