With respect to structure, reference, syntactic category, word
sense
What sort of information is needed to disambiguate
Possibly uninterpretable by people Well, did you do it?
Disambiguated with other sentences or extra-linguistic context And then I told her that was too much to ask. Why are you wearing THAT? He knocked her flat. She left her husband for the garbageman. I saw the numb skull just the other day.
Disambiguated by sentence-level semantics or world knowledge It's hard to eat pizza with chopsticks.
Locally ambiguous, disambiguated eventually by syntax, morphology,
(or semantics)
garden-path sentences The soup pot covers are missing. The inexperienced band together. Have the students who missed the exam take it today. The astronomer married the star.
Dealing with Ambiguity
What people do (maybe)
Preferences: right association, minimal attachment, lexical The man kept the dog in the house. We painted all the walls with cracks. Mary said that Sharon left in her car.
Options
Backtracking in a depth-first parser
Maintaining multiple hypotheses in a breadth-first parser
Limited lookahead (Marcus parser)
Deterministic (no backtracking)
Parse stack, buffer 3 items long (some exceptions)
Input items pass into buffer
Production system takes actions on the basis of the current
parse-treen node and the content of the buffer