Notes on computational linguistics.pdf - UCLA Department of ...

Stabler - Lx 185/209 2003
7.2 Tree collection
7.2.1 Collecting trees: first idea
(9) The most obvious way to collect trees is this:
/* ckyCollect.pl
* E Stabler, Feb 2000
* collect a tree from a CKY parser chart
*/
:- op(1200,xfx,:˜). % this is our object language "if"
:- use_module(library(lists),[member/2]).
ckyCollect(Chart,N,S,S/STs) :- collectTree(Chart,0,S,N,S/STs).
collectTree(Chart,I,A,J,A/Subtrees) :- member((I,A,J),Chart), (A :˜ L), collectTrees(L,Chart,I,J,Subtrees).
collectTree(Chart,I,A,J,A/[]) :- member((I,A,J),Chart), $\backslash$+((A :˜ _)).
collectTrees([],_,I,I,[]).
collectTrees([A|As],Chart,I,J,[A/ATs|Ts]) :- collectTree(Chart,I,A,K,A/ATs), collectTrees(As,Chart,K,J,Ts).
(10) With this file, we can have sessions like this:
Process prolog finished
SICStus 3.8.1 (x86-linux-glibc2.1): Sun Feb 20 14:49:19 PST 2000
Licensed to humnet.ucla.edu
| ?- [ckySics].
{consulting /home/es/tex/185-00/ckySics.pl...}
{consulted /home/es/tex/185-00/ckySics.pl in module user, 260 msec 46700 bytes}
yes
| ?- [ckyCollect].
{consulting /home/es/tex/185-00/ckyCollect.pl...}
{consulted /home/es/tex/185-00/ckyCollect.pl in module user, 20 msec 24 bytes}
yes
| ?- [g1].
{consulting /home/es/tex/185-00/g1.pl...}
{consulted /home/es/tex/185-00/g1.pl in module user, 20 msec 2816 bytes}
yes
| ?- [pp_tree].
{consulting /home/es/tex/185-00/pp_tree.pl...}
{consulted /home/es/tex/185-00/pp_tree.pl in module user, 20 msec 1344 bytes}
yes
| ?- computeClosure([the,idea,will,suffice],Chart),nl,ckyCollect(Chart,4,ip,T),pp_tree(T).
....:.:.:.:.::.::.:.:.:.:.:.::.:
ip /[
dp /[
d1 /[
d0 /[
the /[]],
np /[
n1 /[
n0 /[
idea /[]]]]]],
i1 /[
i0 /[
will /[]],
vp /[
v1 /[
v0 /[
suffice /[]]]]]]
T = ip/[dp/[d1/[d0/[the/[]],np/[n1/[...]]]],i1/[i0/[will/[]],vp/[v1/[v0/[...]]]]],
Chart = [(0,d0,1),(0,d1,2),(0,dp,2),(0,ip,4),(0,the,1),(1,idea,2),(1,n0,2),(1,n1,2),(1,...,...),(...,...)|...] ? ;
no
| ?-
(11) This works, but it makes tree collection almost as hard as parsing!
When we are collecting the constituents, this collection strategy will sometimes follow blind alleys.
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