Browsing by Author "Kourie, Derrick G."

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    An assessment of algorithms for deriving failure deterministic finite automata
    (South African Institute of Computer Scientists and Information Technologists, 2017) Nxumalo, Madoda; Kourie, Derrick G.; Cleophas, Loek; Watson, Bruce W.
    Failure deterministic finite automata (FDFAs) represent regular languages more compactly than deterministic finite automata (DFAs). Four algorithms that convert arbitrary DFAs to language-equivalent FDFAs are empirically investigated. Three are concrete variants of a previously published abstract algorithm, the DFA-Homomorphic Algorithm (DHA). The fourth builds a maximal spanning tree from the DFA to derive what it calls a delayed input DFA. A first suite of test data consists of DFAs that recognise randomised sets of finite length keywords. Since the classical Aho-Corasick algorithm builds an optimal FDFA from such a set (and only from such a set), it provides benchmark FDFAs against which the performance of the general algorithms can be compared. A second suite of test data consists of random DFAs generated by a specially designed algorithm that also builds language-equivalent FDFAs, some of which may have non-divergent cycles. These random FDFAs provide (not necessarily tight) lower bounds for assessing the effectiveness of the four general FDFA generating algorithms.
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    Quality in software development : a pragmatic approach using metrics
    (South African Institute of Computer Scientists and Information Technologists, 2014-07) Acton, Daniel; Kourie, Derrick G.; Watson, Bruce W.
    As long as software has been produced, there have been efforts to strive for quality in software products. In order to understand quality in software products, researchers have built models of software quality that rely on metrics in an attempt to provide a quantitative view of software quality. The aim of these models is to provide software producers with the capability to define and evaluate metrics related to quality and use these metrics to improve the quality of the software they produce over time. The main disadvantage of these models is that they require effort and resources to define and evaluate metrics from software projects. This article briefly describes some prominent models of software quality in the literature and continues to describe a new approach to gaining insight into quality in software development projects. A case study based on this new approach is described and results from the case study are discussed.
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    Weak factor automata : the failure of failure factor oracles?
    (South African Institute of Computer Scientists and Information Technologists, 2014-08) Cleophas, Loek; Kourie, Derrick G.; Watson, Bruce W.
    In indexing of, and pattern matching on, DNA and text sequences, it is often important to represent all factors of a sequence. One efficient, compact representation is the factor oracle (FO). At the same time, any classical deterministic finite automata (DFA) can be transformed to a so-called failure one (FDFA), which may use failure transitions to replace multiple symbol transitions, potentially yielding a more compact representation. We combine the two ideas and directly construct a failure factor oracle (FFO) from a given sequence, in contrast to ex post facto transformation to an FDFA. The algorithm is suitable for both short and long sequences. We empirically compared the resulting FFOs and FOs on number of transitions for many DNA sequences of lengths 4 − 512, showing gains of up to 10% in total number of transitions, with failure transitions also taking up less space than symbol transitions. The resulting FFOs can be used for indexing, as well as in a variant of the FO-using backward oracle matching algorithm. We discuss and classify this pattern matching algorithm in terms of the keyword pattern matching taxonomies of Watson, Cleophas and Zwaan. We also empirically compared the use of FOs and FFOs in such backward reading pattern matching algorithms, using both DNA and natural language (English) data sets. The results indicate that the decrease in pattern matching performance of an algorithm using an FFO instead of an FO may outweigh the gain in representation space by using an FFO instead of an FO.