Hidden Markov Model, Maximum Entropy Hidden Markov Model and Conditional Random Field

Thanks Peng Xu for teaching me about these three models. The differences between them are as follows:

  1. HMM: arrow from st-1 to st, and from st to ot
  2. Maximum Entropy HMM: arrow from st-1 to st, but from ot to st
  3. CRF: no arrow between st-1 and st, neither between st and ot

References:

  1. Andrew Mccallum, Dayne Freitag, Fernando Pereira. Maximum entropy Markov models for information extraction and segmentation, ICML 2000.