I have been working in the field of NLP for several years, and I completely agree with those who provided answers / comments. This is really a hard nut to crack! But let me provide some pointers:
(1) : , - , , , , . : . -, / . .
(2) : . PCFG ( TAG. TAG = , CFG).
(3) : , Wordnet, . . , , ( ) " ", .