Compact DFA Representation for Fast Regular Expression Search

We present a new technique to encode a deterministic nite automaton (DFA). Based on the speciic properties of Glushkov's nondeterministic nite automaton (NFA) construction algorithm, we are able to encode the DFA using (m + 1)(2 m+1 + jj) bits, where m is the number of characters (excluding operator symbols) in the regular expression and is the alphabet. This compares favorably against the worst case of (m+1)2 m+1 jj bits needed by a classical DFA representation and m(2 2m+1 + jj) bits needed by the Wu and Manber approach implemented in Agrep. Our approach is practical and simple to implement, and it permits searching regular expressions of moderate size (which include most cases of interest) faster than with any previously existing algorithm, as we show experimentally.