Saunders, C; Shawe-Taylor, J; Vinokourov, A; (2003) UNSPECIFIED In: (Proceedings) String Kernels, Fisher Kernels and Finite State Automata.
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In this paper we show how the generation of documents can be thought of as a k-stage Markov process, which leads to a Fisher kernel from which the n-gram and string kernels can be re-constructed. The Fisher kernel view gives a more flexible insight into the string kernel and suggests how it can be parametrised in a way that reflects the statistics of the training corpus. Furthermore, the probabilistic modelling approach suggests extending the Markov process to consider sub-sequences of varying length, rather than the standard fixed-length approach used in the string kernel. We give a procedure for determining which sub-sequences are informative features and hence generate a Finite State Machine model, which can again be used to obtain a Fisher kernel. By adjusting the parametrisation we can also influence the weighting received by the features. In this way we are able to obtain a logarithmic weighting in a Fisher kernel. Finally, experiments are reported comparing the different kernels using the standard Bag of Words kernel as a baseline
|Event:||String Kernels, Fisher Kernels and Finite State Automata|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Computer Science|
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