by trying to build from the root node S to the leaves. (example) S → NP VP → DET N VP → the N VP → the cat VP → the cat V N ... → the cat catchs the mouse. (This shows that the sentence is deviated by the grammar.)
input, applying rules from the grammar, and tries to build trees from the words. (example) the cat catchs the mouse. ... → the cat V N → the cat VP → the N VP → DET N VP → NP VP → S (Deviation of S shows the input sentence is grammatical; accepted by the given grammar.)
language grammars – and other ambiguous grammars in order to parse efficiently. • uses the dynamic programming (DP) approach – partial hypothesized results are stored in a structure called a chart and can be re-used. – This eliminates backtracking and prevents a combinatorial explosion.
used within each rule, that indicates the progress of rule analysis. (Example) S → ・ NP VP Nothing is parsed. S → NP ・ VP NP is parsed successfully and S is made when it follows VP. S → NP VP ・ Analysis is finished to make S. A solid line is used.
algorithm. Also called as CKY algorithm. • is very efficient; a bottom-up dynamic programming parsing algorithm. • can be used if all rules are written in Chomsky normal form / チョムスキー標準形 : – A → BC or A → α where A, B, and C are non-terminals, and α is terminal. (I will demonstrate how it works.)
VP PP → N P VP → PP VP VP → V AUXV (Rules are slightly changed in order to meet requirement of Chomsky normal form. Compare to two slides before.) N → カレー (curry) P → を (OBJ) V → 食べ (to eat) AUXV → た (PAST)