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Table 2 Feature templates used in the CRF tagger

From: Accelerating the annotation of sparse named entities by dynamic sentence selection

Word Unigram w i , wi-1, wi+1 &y i
POS Unigram p i , pi-1, pi+1 &y i
Prefix, Suffix prefixes of w i &y i
  suffixes of w i &y i
  (up to length 3)  
Normalized Word N(w i ) &y i
Word Shape S(w i ) &y i
Tag Bi-gram true &yi-1y i