1. 11 An Improved Algorithm to Accelerate Regular Expression Evaluation Authors: Michela Becchi and Patrick Crowley Publisher: ANCS’07 Present: Kia-Tso Chang Date: January 8 2008

2. 2 outline D 2 FA The proposal Reducing the alphabet Experimental evaluation

3. 3 Default transition

4. 4 D 2 FA(diameter bound of 4)

5. 5 5

6. 6 D 2 FA(diameter bound of 2)

7. 7 Lemma we define its depth as the minimum number of states visited when moving from s0 to s in the DFA. Lemma: If none of the default transitions in a D2FA lead from a state with depth di to a state of depth dj with dj ≥ di, then any string of length N will require at most 2N state traversals to be processed.

8. 8 The proposal

9. 9

10. 10 Reducing the alphabet Two symbols ci and cj will fall into the same class if they are treated the same way in all DFA states. In other words, given the transition function δ(states, Σ)→states,δ(s,ci)= δ(s,cj) for each state s belonging to the DFA

11. 11 Two observations

12. 12 Experimental evaluation

13. 13 Experimental evaluation