CSA350: NLP Algorithms. Sentence Parsing I The Parsing Problem Parsing as Search Top Down/Bottom Up Parsing Strategies. References. This lecture is based on material found in Jurafsky & Martin chapter 10 Relevant material available from Vince.
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CSA350: NLP Algorithms
Sentence Parsing I
The Parsing Problem
Parsing as Search
Top Down/Bottom Up Parsing
Strategies
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
s--> np, vp.
s --> aux, np, vp.
s --> vp.
np --> det nom.
nom --> noun.
nom --> noun, nom.
nom --> nom, pp
pp --> prep, np.
np --> pn.
vp --> v.
vp --> v np
d --> [that];[this];[a].
n --> [book];[flight];
[meal];[money].
v-->
[book];[include]; [prefer].
aux --> [does].
prep --> [from];[to];[on].
pn --> [‘Houston’];[‘TWA’].
csa3180: Parsing Algorithms 1
A valid parse tree for a grammar G is a tree
csa3180: Parsing Algorithms 1
Given grammar G and sentence A find all valid parse trees for G that exactly cover A
S
VP
NP
V
Nom
Det
book
N
that
flight
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
Start node→
Goal node
↓
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
fl
fl
fl
fl
fl
fl
fl
csa3180: Parsing Algorithms 1
Top down
For: Never wastes time exploring trees that cannot be derived from S
Against: Can generate trees that are not consistent with the input
Bottom up
For: Never wastes time building trees that cannot lead to input text segments.
Against: Can generate subtrees that can never lead to an S node.
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1
csa3180: Parsing Algorithms 1