- Though rule-based systems exist, typically NER is framed as a supervised learning problem. Take a look at sequence tagging models (HMM, CRF, RNN, LSTM, etc.).
- For feature-based models, here are few commonly used features:
- word shape for encoding capitalization (ex. Bob -> Xxx, Virginia -> Xxx)
- PoS tag
- prefix and suffix
- the same features for surrounding words