August 17, 2005
Generic Soft Pattern Models for
Definitional QA
18/28
Estimation of PHMM
•Estimated
by Baum-Welch algorithm
–Using
the most probable path during training
•Random
or uniform initialization may lead to unsatisfactory model
–Extreme
diversity of definition patterns and not sufficient training
data
–Assume
path should favor match states over others
•P(
token | Match ) > P ( token | Insertion )
–Using
smoothed ML estimates