Paddy Nixon

University of Tasmania, Hobart Town, Tasmania, Australia

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Publications (173)19.23 Total impact

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    ABSTRACT: One of the many challenges faced when evaluating context-aware ubiquitous systems is to gain some understanding of the constant influx of context data into the system. Else-where, context has been distilled into more natural abstrac-tions called situations with the aim of making these sys-tems more understandable and intuitive to develop appli-cations for, though codifying and manipulating these situ-ations still presents problems. We introduce Situvis, a tool we have developed based on the Parallel Coordinates Visual-isation technique, which assists users by visually represent-ing the conditions that need to be present for a situation to be triggered in terms of the real-world context that is being recorded in their system, and allows the user to visually in-spect these properties, evaluate their correctness, and change them as required. We describe the use of our tool with a small user study.
  • Emerson Loureiro · Paddy Nixon · Simon Dobson
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    ABSTRACT: Resource pools are collections of computational resources (e.g., servers) which can be used by different applications in a shared way. A crucial aspect in these pools is to allocate resources so as to ensure their proper usage, taking into account workload and specific requirements of each application. An interesting approach, in this context, is to allocate the resources in the best possible way, aiming at optimal resource usage. Workload, however, varies over time, and in turn, resource demands will vary too. To ensure that optimal resource usage is always in place, resource shares should be defined dynamically and over time. It has been claimed that utility functions are the main tool for enabling such self-optimizing behavior. Whereas many solutions with this characteristic have been proposed to date, none of them presents true decentralization within the context of shared pools. In this article, we then propose a decentralized model for optimal resource usage in shared resource pools, providing practical and theoretical evidence of its feasibility.
    ACM Transactions on Autonomous and Adaptive Systems 04/2012; 7(1). DOI:10.1145/2168260.2168274 · 0.79 Impact Factor
  • Benoit Gaudin · Paddy Nixon
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    ABSTRACT: The Supervisory Control Theory (SCT) introduced by Ramadge and Wonham offers a framework for the control of Discrete Event Systems. In this paper, we formalize some concepts about corrective software maintenance within this framework. More specifically, we consider SCT as a way to control software systems behaviors and avoid occurrences of runtime exceptions. This approach is attractive as algorithms for controllers synthesis offer a means to automate part of the corrective maintenance process. In this paper, we introduce problems related to removing observed software failures by control, as well as solutions.
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    Neil Cowzer · Paddy Nixon
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    ABSTRACT: Publish-subscribe systems are well suited loosely decoupled nature of the web, resulting in the messaging paradigm gaining widespread adoption and being the subject of much research. Such research has focused primarily on architectures and filtering algorithms with little evidence of performance analysis or characterization of user behavior in these widely deployed messaging paradigms. In this paper we discuss and examine implicit group messaging; an application-layer many-to-many messaging paradigm for delivering messages from publishers to specified groups of consumers. Such consumer groups are not addressed by explicit names, instead they are reached by describing the shared attributes or interests of consumers, forming easily defined implicit groups. Based on a 4 week experiment we analyze the characteristics of implicit groups and their usage. We find implicit group messaging workload to be similar to RSS in terms of group membership and update patterns; groups are typically small with few large examples and update rates vary from infrequent to more limited intervals.
    GLOBECOM Workshops (GC Wkshps), 2010 IEEE; 01/2011
  • Emil Vassev · Mike Hinchey · Benoit Gaudin · Paddy Nixon
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    ABSTRACT: Autonomic Service-Component Ensembles (ASCENS) is a class of multi-agent systems formed as mobile, intelligent and open-ended swarms of special autonomic service components capable of local and distributed reasoning. Such components encapsulate rules, constraints and mechanisms for self-adaptation and acquire and process knowledge about themselves, other service components and their environment. ASCENS systems pose distinct challenges for knowledge representation languages. In this paper, we present requirements and an initial model for such a language called KnowLang. KnowLang is intended to provide for formal specification of distinct knowledge models each representing a different knowledge domain of an ASCENS system, such as the internal world of a service component, the world of a service-component ensemble, the surrounding external world and information of special situations related to state changes and operations of service components. KnowLang provides the necessary constructs and mechanisms for specifying such knowledge models at two main levels -- an ontology level and a logic-foundations level, where the latter is formed by special facts, rules, constraints and inter-ontology operators. In this paper, we also survey one of the ASCENS case studies to derive some of the requirements for KnowLang.
    Fourth International C* Conference on Computer Science & Software Engineering, C3S2E 2011, Montreal, Quebec, Canada, May 16-18, 2011, Proceedings; 01/2011
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    Ross Shannon · Aaron J. Quigley · Paddy Nixon
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    ABSTRACT: Software tools are used to compare multiple versions of a textual document to help a reader understand the evolution of that document over time. These tools generally support the comparison of only two versions of a document, requiring multiple comparisons to be made to derive a full history of the document across multiple versions. We present Deep Diffs, a novel visualisation technique that exposes the multiple layers of history of a document at once, directly in the text, highlighting areas that have changed over multiple successive versions, and drawing attention to passages that are new, potentially unpolished or contentious. These composite views facilitate the writing and editing process by assisting memory and encouraging the analysis of collaboratively-authored documents. We describe how this technique effectively supports common text editing tasks and heightens participants' understanding of the process in collaborative editing scenarios like wiki editing and paper writing.
    Proceedings of the International Conference on Advanced Visual Interfaces, AVI 2010, Roma, Italy, May 26-28, 2010; 12/2010
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    ABSTRACT: in a pervasive environment
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    Ross Shannon · Aaron J. Quigley · Paddy Nixon
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    ABSTRACT: Visualisations of dynamic networks are animated over time, reflecting changes in the underlying data structure. As viewers of these visualisations, it is up to us to accurately perceive and keep up with the constantly shifting view, mentally noting as visual elements are added, removed, changed and rearranged, sometimes at great pace. In a complex data set with a lot happening, this can put a strain on the observer's perceptions, with changes in layout and visual population disrupting their internalised mental model of the visualisation, making it difficult to understand what the changes represent. We present Showtime, a novel visualisation technique which dilates the flow of time so that observers have proportionally more time to understand each change based on the density of activity in the visualisation. This is paired with a novel timeline element which tracks the flow of time visually.
    Proceedings of the International Conference on Advanced Visual Interfaces, AVI 2010, Roma, Italy, May 26-28, 2010; 12/2010
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    Ross Shannon · Aaron Quigley · Paddy Nixon
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    ABSTRACT: peer-reviewed Network visualisations use clustering approaches to simplify the presentation of complex graph structures. We present a novel application of clustering algorithms, which controls the visual arrangement of the vertices in a cluster to explicitly encode information about that cluster. Our technique arranges parts of the graph into symbolic shapes, depending on the relative size of each cluster. Early results suggest that this layout augmentation helps viewers make sense of a graph's scale and number of elements, while facilitating recall of graph features, and increasing stability in dynamic graph scenarios. SFI
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    ABSTRACT: Context-aware systems that rely on mobile devices for user interaction must address the low bandwidth of both communications and more importantly the user's limited attention, which will typically be split between several com-peting tasks. Content delivery in such systems must be adapted closely to users' evolving situations and shifting priorities, in a way that cannot be accomplished using static filtering determined a priori. We propose a more dynamic context-driven approach to content delivery, that integrates information from a wide range of sources. We demonstrate our approach on a system for adaptive message pri-oritisation and forwarding.
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    Emerson Loureiro · Paddy Nixon · Simon Dobson
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    ABSTRACT: Resource pools are collections of computational resources which can be shared by different applications. The goal with that is to accommodate the workload of each application, by splitting the total amount of resources in the pool among them. In this sense, utility functions have been pointed as the main tool for enabling self-optimizing behaviour in such pools. The goal with that is to allow resources from the pool to be split among applications, in a way that the best outcome is obtained. Whereas different solutions in this context exist, it has been found that none of them tackles the problem we deal with in a total decentralized way. In this paper, we then present a decentralized and self-optimizing approach for resource management in shared resource pools.
    10/2010: pages 149-170;
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    ABSTRACT: Pervasive systems are large-scale systems consisting of many sensors capturing numerous types of information. As this data is highly voluminous and dimensional, data analysis tasks can be extremely cumbersome and time-consuming. Enabling computers to recognise real-world situations is an even more difficult problem, involving not only data analysis, but also consistency checking. Here we present Situvis, an interactive visualisation tool for representing sensor data and creating higher-level abstractions from the data. This paper builds on previous work, Clear et al. (2009) [8] through evolved tool functionality and an evaluation of Situvis. A user-trial consisting of 10 participants shows that Situvis can be used to complete the key tasks in the development process of situation specifications in over 50% less time than an improvised alternative toolset.
    Pervasive and Mobile Computing 10/2010; 6:575-589. DOI:10.1016/j.pmcj.2010.04.002 · 1.67 Impact Factor
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    Emil Vassev · Mike Hinchey · Paddy Nixon
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    ABSTRACT: Intelligent swarms draw their inspiration from biology where many simple entities act independently, but when grouped, they appear to be highly organized. NASA is currently investigating swarm-based technologies for the development of prospective exploration missions to explore regions of space where a single large spacecraft would be impractical. The main emphasis of this research is to develop algorithms and prototyping models for self-managing swarm-based space-exploration systems. This article presents our work on formally modeling self-configuring behavior in such systems. We present a formal model for team formation based on Partially Observable Markov Decision Processes and Discrete Time Markov Chains along with formal models for planning and scheduling.
    Adaptive Hardware and Systems (AHS), 2010 NASA/ESA Conference on; 07/2010
  • Newres Al Haider · Paddy Nixon · Benoit Gaudin
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    ABSTRACT: In this paper we present the possibility of using an ontology based framework in order to model Dynamic Analysis techniques. This work relies on similar ideas applied to the case of Static Analysis [22, 28, 27], in which ontologies are used to represent some knowledge about the programs to be analyzed. In the approach proposed in this paper we describe how ontologies can be applied to Dynamic Analysis by modeling both the information collected from the system, as well as some requirements about the type of analysis to be performed. Both of these ontologies can be designed by integrating ontologies previously defined during the software development cycle, allowing for re-usability. Finally, these ontologies make it possible to reason about concepts related to Dynamic Analysis and offer tools that facilitate automation. This paper presents the main ideas of the proposed approach and illustrates them with an example related to Frequency Spectrum Analysis.
    Proceedings of the Eighth International Workshop on Dynamic Analysis; 07/2010
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    E. Vassev · P. Nixon
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    ABSTRACT: We describe the use of ASSL (Autonomic System Specification Language) and DMF (Demand Migration Framework) in the development of software systems for intelligent sensor networks. ASSL is used to formally specify and automatically generate autonomous intelligent sensor nodes. DMF is applied to connect those nodes in a sensor network. ASSL provides sensor networks with self-management behavior based on special policies allowing sensor nodes to reason and collaborate by exchanging information via a DMF instance.
    Collaborative Technologies and Systems (CTS), 2010 International Symposium on; 06/2010
  • Graeme Stevenson · Juan Ye · Simon Dobson · Paddy Nixon
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    ABSTRACT: Location is a core concept in most pervasive systems-and one that's surprisingly hard to deal with flexibly. Using a location model supporting a range of expressive representations for spaces, spatial relationships, and positioning systems, the authors constructed LOC8, a programming framework for exploring location data's multifaceted representations and uses. With LOC8, developers can construct complex queries by combining basic queries and additional contextual information.
    IEEE Pervasive Computing 04/2010; 9(1-9):28 - 37. DOI:10.1109/MPRV.2009.90 · 2.10 Impact Factor
  • Simon Dobson · Roy Sterritt · Paddy Nixon · Mike Hinchey
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    ABSTRACT: Efforts since 2001 to design self-managing systems have yielded many impressive achievements, yet the original vision of autonomic computing remains unfulfilled. Researchers must develop a comprehensive systems engineering approach to create effective solutions for next-generation enterprise and sensor systems.
    Computer 02/2010; DOI:10.1109/MC.2010.14 · 1.44 Impact Factor
  • Emil Vassev · Mike Hinchey · Paddy Nixon
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    ABSTRACT: Self-managing policies provide a self-management behavior for autonomic systems developed with ASSL (Autonomic System Specification Language). With ASSL we have successfully developed special autonomic prototypes of both the NASA ANTS (Autonomous Nano-Technology Swarm) concept mission and NASAs Voyager Mission. In these prototypes, we applied ASSL self-managing policies to drive the missions in critical situations in response to environmental or system changes. Therefore, the logical correctness of the ASSL specification of such policies appears to be of major importance. Experience has shown, however, that ASSL specifications may contain logical faults causing improper behavior. To handle such behavior, self-managing policies are often tested with manually injected inputs triggering events and satisfying constraints to allow for the activation, execution, and deactivation of these policies. The logical correctness of an ASSL self managing policy currently depends solely upon the relation between inputs and conclusion. In this paper, we present our initial work on a novel tool, part of the ASSL framework, that generates test cases based on change-impact analysis. Our main goal is to reduce testing costs and effort and improve the quality of testing, thus eventually assuring the logical correctness of the self-managing policies developed with ASSL.
    4th IEEE International Symposium on Theoretical Aspects of Software Engineering, TASE 2010, Taipei, Taiwan, 25-27 August 2010; 01/2010
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    Emil Vassev · Mike Hinchey · Paddy Nixon
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    ABSTRACT: peer-reviewed We target effective home automation based on wireless sensor networks. ASSL (Autonomic System Specification Language) is used to formally specify and generate prototype models for wireless sensor networks controlling a simulated virtual home environment. This approach allows for formal validation, experiments under simulated conditions, and smooth transition from a prototype system to a real one. SFi

Publication Stats

2k Citations
19.23 Total Impact Points

Institutions

  • 2011–2012
    • University of Tasmania
      Hobart Town, Tasmania, Australia
  • 2006–2012
    • University College Dublin
      • School of Computer Science and Informatics
      Dublin, Leinster, Ireland
  • 2002–2006
    • University of Strathclyde
      • Department of Computer and Information Sciences
      Glasgow, Scotland, United Kingdom
  • 2000
    • Trinity College
      • Computer Science
      Hartford, Connecticut, United States
  • 1997–1999
    • Trinity College Dublin
      • Department of Computer Science
      Dublin, Leinster, Ireland