An automatic approach for constructing a knowledge base of symptoms in Chinese

Table 3 Features of CRF

Feature type	Feature contents
Literal features	Unigram	X _i−3, X _i−2, X _i−1,X _i, X _i+1, X _i+2, X _i+3
	Bigram	X _i−3 X _i−2,X _i−2 X _i−1,X _i−1 X _i, X _i X _i+1, X _i+1 X _i+2, X _i+2 X _i+3
	Trigram	X _i−3 X _i−2 X _i−1,X _i−2 X _i−1 X _i, X _i−1 X _i X _i+1,X _i X _i+1 X _i+2, X _i+1 X _i+2 X _i+3
Position features	Index _i
POS features	Unigram	P _i−3, P _i−2, P _i−1, P _i, P _i+1, P _i+2, P _i+3
	Bigram	P _i−3 P _i−2, P _i−2 P _i−1,P _i−1 P _i, P _i P _i+1, P _i+1 P _i+2, P _i+2 P _i+3
	Trigram	P _i−3 P _i−2 P _i−1,P _i−2 P _i−1 P _i, P _i−1 P _i P _i+1,P _i P _i+1 P _i+2, P _i+1 P _i+2 P _i+3

ISSN: 2041-1480