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Published online 2011 June 14. doi: 10.1093/bioinformatics/btr214

Table 3.

Feature templates used in the CRF tagger

Word unigramwi−5, wi−4, wi−3, wi−2, wi−1, wiwi+1, wi+2, wi+3, wi+4, wi+5& yi
Word bigramwi−1wi, wiwi+1& yi
Word trigramwi−1wiwi+1& yi
Substringssubstrings of wi& yi
(up to length 10)
Word shapeS(wi)& yi
Tag bigramTrue& yi−1yi

wi is the current word. yi is the current tag. Word shape S(wi) is produced by converting capital letters into ‘A’, small letters into ‘a’ and numerals into ‘#’.