1. A method of constructing a composite DFA using subset construction, said method comprising: compiling at least one single-rule DFA; performing a first subset construction on said at least one single-rule DFA to generate a first composite DFA, retaining subset information for said first composite DFA; compiling at least one new rule into at least one corresponding additional single-rule DFA; and performing a second subset construction to generate a second composite DFA, wherein said first composite DFA acts as a first NFA input for said second subset construction and said at least one corresponding additional single-rule DFA acts as at least one additional NFA input for said second subset construction, retaining subset information for said second composite DFA.