Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

6) article → a,
7) article → the,
8) noun → man,
9) noun → deer,
10) verb → killed,
11) verb → likes.
It is to be noted from the above set of production (re-write) rules that
the terminals do not appear in the left-hand side of the rules.
The sentence: ‘The man killed a deer’ now can be analyzed by the
following sequence of re-write rules. We here onwards abbreviate noun-phrase
as NP, verb-phrase as VP, noun as N, verb as V and article as ART. Now,
starting with re-write rule 1, we have:
S → NP VP (by 1)
→ ART N VP (by 3)
→ the man VP (by 7 & 8 )
→ the man V NP (by 5)
→ the man killed NP (by 10)
→ the man killed ART N (by 3)
→ the man killed a deer (by 6 & 10)
The above example describes a top-down derivation. It starts with the
sentence symbol S and continues replacing the left-hand side of the selected rewrite
rules by their right-hand side, so that ultimately the complete sentence
appears at the end of the derivation. An alternative form called the bottom-up
derivation starts with the string of the sentential representation and continues
replacing the right-hand side of the re-write rules by their left-hand side until
the starting symbol S is reached.
A tree, called the parse tree, can also represent the derivations
presented above. The parse tree for the sentence under consideration is
presented in fig. 18.1.
Fig.18.1 has similarity with the derivation of the sentence, presented in
example 18.1. It is however observed from fig.18.1 that VP and NP occur
more than once at different levels of the tree. This happened so as we did not
expand VP or NP at its first occurrence. Had it been so, the resulting tree
would look like fig.18.2.