2004 Working Papers

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https://researchcommons.waikato.ac.nz/handle/10289/10041

Now showing 1 - 5 of 14

Atomic components
(Working Paper, University of Waikato, Department of Computer Science, 2004-02) Reeves, Steve; Streader, David
There has been much interest in components that combine the best of state-based and event-based approaches. The interface of a component can be thought of as its specification and substituting components with the same interface cannot be observed by any user of the components. Here we will define the semantics of atomic components where both states and event can be part of the interface. The resulting semantics is very similar to that of (event only) processes. But it has two main novelties: one, it does not need recursion or unique fixed points to model nontermination; and two, the behaviour of divergence is modelled by abstraction, i.e. the construction of the observational semantics.
Unifying state and process determinism
(Working Paper, University of Waikato, Department of Computer Science, 2004-02) Reeves, Steve; Streader, David
If a coin is given to a deterministic robot that interacts with a deterministic vending machine then is the drink that the robot is delivered determined? Using process definitions of determinism from CSP, CCS or ACP the answer is "no", whereas state-based definitions of determinism can reasonably be construed as giving the answer "yes". In order to unify what we see as discrepancies in state- and action-based notions of determinism we will consider process algebras over two sets of actions: the active or casual actions of the robot and the passive or reactive actions of the vending machine. In addition we will add priority to the actions and when two τ actions are possible then the τ action with the highest priority will be executed.
The syntax and semantics of μ-Charts
(Working Paper, University of Waikato, Department of Computer Science, 2004-02) Reeve, Greg; Reeves, Steve
μ-Charts is a language for specifying the behaviour of reactive systems. The language is a simplified variant of the well-known language Statecharts that was introduced by Harel. Development of the μ-Charts language is ongoing research undertaken under the auspices of the Formal Methods Laboratory of the Computer Science Department, University of Waikato. This paper gives a comprehensive treatment of the syntax and semantic for μ-Charts.
DeepDocument: use of a multi-layered display to provide context awareness in text editing
(Working Paper, University of Waikato, Department of Computer Science, 2004-02) Masoodian, Masood; McKoy, Sam; Rogers, Bill; Ware, David
The most commonly used view in word processing software shows only the paragraphs of text immediately adjacent to the cursor position. Generally this is appropriate, for example when composing a single paragraph. However, when reviewing or working on the layout of a document it is necessary to establish awareness of current text in the context of the document as a whole. This can be done by scrolling or zooming, but when doing so, focus is easily lost and hard to regain. Furthermore, in a collaborative editing/review setting it is not only necessary for each user to understand their own context, but also to have an awareness of the contexts of the other participants. Although systems have been developed that provide awareness in collaborative settings, they usually rely on multiple windows, which use valuable screen real-estate. We have developed a system called DeepDocument using a two-layered LCD display in which both focussed and document-wide views are presented simultaneously. The overview is shown on the rear display and the focussed view on the front, maintaining full screen size for each. The physical separation of the layers takes advantage of human depth perception capabilities to allow users to perceive the views independently without having to redirect their gaze. DeepDocument has been written as an extension to Microsoft Word™. It also includes awareness features to track focus positions for both single and multiple users.
Ensembles of nested dichotomies for multi-class problems
(Working Paper, University of Waikato, Department of Computer Science, 2004-02) Frank, Eibe; Kramer, Stefan
Nested dichotomies are a standard statistical technique for tackling certain polytomous classification problems with logistic regression. They can be represented as binary trees that recursively split a multi-class classification task into a system of dichotomies and provide a statistically sound way of applying two-class learning algorithms to multi-class problems (assuming these algorithms generate class probability estimates). However, there are usually many candidate trees for a given problem and in the standard approach the choice of a particular tree is based on domain knowledge that may not be available in practice. An alternative is to treat every system of nested dichotomies as equally likely and to form an ensemble classifier based on this assumption. We show that this approach produces more accurate classifications than applying C4.5 and logistic regression directly to multi-class problems. Our results also show that ensembles of nested dichotomies produce more accurate classifiers than pairwise classification if both techniques are used with C4.5, and comparable results for logistic regression. Compared to error-correcting output codes, they are preferable if logistic regression is used, and comparable in the case of C4.5. An additional benefit is that they generate class probability estimates. Consequently they appear to be a good general-purpose method for applying binary classifiers to multi-class problems.

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