2006 Working Papers

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  • Publication
    Proceedings of the second computing women congress: Student Papers
    (Working Paper, University of Waikato, Department of Computer Science, 2006-02-11) Hinze, Annika; Jung, Doris; Cunningham, Sally Jo
    The CWC 2006 Proceedings contains the following student papers: • Kathryn Hempstalk: Hiding Behind Corners: Using Edges in Images for Better Steganography • Supawan Prompramote, Kathy Blashki: Playing to Learn: Enhancing Educational Opportunities using Games Technology • Judy Bowen: Celebrity Death Match: Formal Methods vs. User-Centred Design • Liz Bryce: BECOMING INDIGENOUS: an impossible necessity • Tatiana King: Privacy Issues in Health Care and Security of Statistical Databases • Nilufar Baghaei: A Collaborative Constraint-based Intelligent System for Learning Object-Oriented Analysis and Design using UML • Sonja van Kerkhof: Alternatives to stereotypes: some thoughts on issues and an outline of one game
  • Publication
    LSB - Live and Safe B: Alternative semantics for Event B
    (Working Paper, Department of Computer Science, University of Waikato, 2006-07-01) Reeves, Steve; Streader, David
    We define two lifted, total relation semantics for Event B machines: Safe B for safety-only properties and Live B for liveness properties. The usual Event B proof obligations, Safe, are sufficient to establish Safe B refinement. Satisfying Safe plus a simple additional proof obligation ACT REF is sufficient to establish Live B refinement. The use of lifted, total relations both prevents the ambiguity of the unlifted relational semantics and prevents operations being clairvoyant.
  • Publication
    Arbitrary boolean advertisements: the final step in supporting the boolean publish/subscribe model
    (Working Paper, Department of Computer Science, University of Waikato, 2006-06-01) Bittner, Sven; Hinze, Annika
    Publish/subscribe systems allow for an efficient filtering of incoming information. This filtering is based on the specifications of subscriber interests, which are registered with the system as subscriptions. Publishers conversely specify advertisements, describing the messages they will send later on. What is missing so far is the support of arbitrary Boolean advertisements in publish/subscribe systems. Introducing the opportunity to specify these richer Boolean advertisements increases the accuracy of publishers to state their future messages compared to currently supported conjunctive advertisements. Thus, the amount of subscriptions forwarded in the network is reduced. Additionally, the system can more time efficiently decide whether a subscription needs to be forwarded and more space efficiently store and index advertisements. In this paper, we introduce a publish/subscribe system that supports arbitrary Boolean advertisements and, symmetrically, arbitrary Boolean subscriptions. We show the advantages of supporting arbitrary Boolean advertisements and present an algorithm to calculate the practically required overlapping relationship among subscriptions and advertisements. Additionally, we develop the first optimization approach for arbitrary Boolean advertisements, advertisement pruning. Advertisement pruning is tailored to optimize advertisements, which is a strong contrast to current optimizations for conjunctive advertisements. These recent proposals mainly apply subscription-based optimization ideas, which is leading to the same disadvantages. In the second part of this paper, our evaluation of practical experiments, we analyze the efficiency properties of our approach to determine the overlapping relationship. We also compare conjunctive solutions for the overlapping problem to our calculation algorithm to show its benefits. Finally, we present a detailed evaluation of the optimization potential of advertisement pruning. This includes the analysis of the effects of additionally optimizing subscriptions on the advertisement pruning optimization.
  • Publication
    State- and event-based refinement
    (Working Paper, Department of Computer Science, University of Waikato, 2006-09-01) Reeves, Steve; Streader, David
    In this paper we give simple example abstract data types, with atomic operations, that are related by data refinement under a definition used widely in the literature, but these abstract data types are not related by singleton failure refinement. This contradicts results found in the literature. Further we show that a common way to change a model of atomic operations to one of value passing operations actually changes the underlying atomic operational semantics.
  • Publication
    A Taxonomy of model-based testing
    (Working Paper, Department of Computer Science, University of Waikato, 2006-04-01) Utting, Mark; Pretschner, Alexander; Legeard, Bruno
    Model-based testing relies on models of a system under test and/or its environment to derive test cases for the system. This paper provides an overview of the field. Seven different dimensions define a taxonomy that allows the characterization of different approaches to model-based testing. It is intended to help with understanding benefits and limitations of model-based testing, understanding the approach used in a particular model-based testing tool, and understanding the issues involved in integrating model-based testing into a software development process. To illustrate the taxonomy, we classify several approaches embedded in existing model-based testing tools.
  • Publication
    A Decision tree-based attribute weighting filter for naive Bayes
    (Working Paper, 2006-05-01) Hall, Mark A.
    The naive Bayes classifier continues to be a popular learning algorithm for data mining applications due to its simplicity and linear run-time. Many enhancements to the basic algorithm have been proposed to help mitigate its primary weakness--the assumption that attributes are independent given the class. All of them improve the performance of naïve Bayes at the expense (to a greater or lesser degree) of execution time and/or simplicity of the final model. In this paper we present a simple filter method for setting attribute weights for use with naive Bayes. Experimental results show that naive Bayes with attribute weights rarely degrades the quality of the model compared to standard naive Bayes and, in many cases, improves it dramatically. The main advantages of this method compared to other approaches for improving naive Bayes is its run-time complexity and the fact that it maintains the simplicity of the final model.
  • Publication
    Computational sense: the role of technology in the education of digital librarians
    (Working Paper, Department of Computer Science, University of Waikato, 2006-10-01) Twidale, Michael B.; Nichols, David M.
    The rapid progress of digital library technology from research to implementation has created a force for change in the curricula of library schools. The education of future librarians has always had to adapt to new technologies but the pace, complexity and implications of digital libraries pose considerable challenges. In this article we explore how we might successfully blend elements of computer science and library science to produce effective educational experiences for the digital librarians of tomorrow. We first outline the background to current digital librarian education and then propose the concept of computational sense as an appropriate meeting point for these two disciplines.
  • Publication
    Subscription tree pruning: A structure-independent routing optimization for general-purpose publish/subscribe systems.
    (Working Paper, Department of Computer Science, 2006-01-01) Bittner, Sven; Hinze, Annika
    A main challenge in distributed publish/subscribe systems is the efficient and scalable routing of incoming information (event messages). For largescale publish/subscribe services, subscription forwarding has been established as a prevalent routing scheme. It reduces the network traffic for event routing due to selectively forwarding event messages to relevant parts of the network only. To further improve event routing, publish/subscribe systems apply routing optimizations. So far, optimizations for general-purpose publish/subscribe systems are still missing. In this paper, we present the architecture, realization, and evaluation of our prototype of a large-scale publish/subscribe service applying a novel routing optimization, subscription tree pruning. We also show a comparison of five existing routing optimizations in respect to six important characteristic parameters affecting the suitability of these approaches in practice (including space usage, time efficiency (throughput), and network load). This comparative analysis clearly demonstrates the advantages of subscription pruning over other routing optimizations. In our practical experiments, we then investigate the behavior of our prototype regarding all quantitatively measurable parameters from our previously theoretically analyzed ones. Our evaluation of subscription pruning in this paper is more extensive than previous analyses of any routing optimizations for publish/ subscribe systems, which focus on selected parameters only.
  • Publication
    Liberalising Event B without changing it
    (Working Paper, Department of Computer Science, University of Waikato, 2006-07-01) Reeves, Steve; Streader, David
    We transfer a process algebraic notion of refinement to the B method by using the well-known bridge between the relational semantics underlying the B machines and the labelled transition system semantics of processes. Thus we define delta refinement on Event B systems. We then apply this new refinement to a problem from the literature that previously could only be solved by retrenchment.
  • Publication
    Event distributions in online book auctions.
    (Working Paper, University of Waikato, 2006-02-01) Bittner, Sven; Hinze, Annika
    Current quantitative evaluations in various research areas for publish/ subscribe systems use artificially created event messages to model the system workload. The assumptions made to create these workloads are rather strong and hardly ever described in detail. This does not allow for a repetition of experiments or comparative evaluations of different approaches by different researches. In this paper, we present an evaluation of the distributions of the values of attributes typically used in online auction scenarios. In particular, we focus on auctions of fiction books. We further show our approach of creating event messages by the help of the gained information. Publishing this information on how to create a typical workload for online auctions should allow for the repetition of experiments and the comparison of different evaluations.