Combining PPM models using a text mining approach


: This paper introduces a novel switching method which can be used to combine two or more PPM models. The work derives from our earlier work on modelling English and text mining, and the approach takes advantage of both to help improve the compression performance signicantly. The performance of the combination of models is at least as good as (and in many cases signicantly better than) the best performed of the individual models. 1 Introduction The PPM data compression scheme has consistently set the standard in lossless compression of text since it was originally described by Cleary & Witten back in 1984. Moat's (1990) implementation, PPMC, set the benchmark for over a decade, and currently, an implementation of the PPMD algorithm (Howard, 1993) has the distinction of being the best \all-round" compression scheme (ACT, 2000). Other variations on a very productive research theme include improved blending algorithms (Bunton, 1996), improved escape estimation for the nely tun..

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