Datensatz

Zusammenfassung

A popular and well-studied class of filters for approximate string matching compares substrings of length $q$, \emph{the $q$-grams}, in the pattern and the text to identify text areas that contain potential matches. A generalization of the method that uses {\em gapped} $q$-grams instead of contiguous substrings is mentioned a few times in literature but has never been analyzed in any depth. In this paper, we report the first results of a study on gapped $q$-grams. We show that gapped $q$-grams can provide orders of magnitude faster and/or more efficient filtering than contiguous $q$-grams. To achieve these results the arrangement of the gaps in the $q$-gram and a filter parameter called \emph{threshold} have to be optimized. Both of these tasks are nontrivial combinatorial optimization problems for which we present efficient solutions. We concentrate on the $k$~mismatches problem, i.e, approximate string matching with the Hamming distance.