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

Stabler - Lx 185/209 2003
(18) Throughout our study, we will keep an eye on these basic properties of syntactic analysis algorithms
which are mentioned in these facts:
1. First, we would like our deductive system to be sound (if s can be derived from A, thencan be
deduced from axioms s and goal ?-A) and complete (if can be deduced from axioms s and goal ?-A,
then s can be derived from A), and we also prefer to avoid spurious ambiguity. That is, we would
like there to be n proofs just in case there are n corresponding derivations from the grammar.
2. Furthermore, we would prefer for there to be a substantial subset of the language that can be recognized
with finite memory.
3. Finally, we would like the search space for any particular input to be finite.
(19) Let’s call the grammar considered earlier, G1, implemented in g1.pl as follows:
:- op(1200,xfx,:˜).
ip :˜ [dp, i1]. i1 :˜ [i0, vp]. i0 :˜ [will].
dp :˜ [d1]. d1 :˜ [d0, np]. d0 :˜ [the].
np :˜ [n1]. n1 :˜ [n0]. n0 :˜ [idea].
n1 :˜ [n0, cp].
vp :˜ [v1]. v1 :˜ [v0]. v0 :˜ [suffice].
cp :˜ [c1]. c1 :˜ [c0, ip]. c0 :˜ [that].
(20) Let’s call this top-down, backtracking recognizer, considered last time, td.pl:
/*
* file: td.pl = ll.pl
*
*/
:- op(1200,xfx,:˜ ). % this is our object language "if"
:- op(1100,xfx,?˜ ). % metalanguage provability predicate
[] ?˜ [].
(S0 ?˜ Goals0) :- infer(S0,Goals0,S,Goals), (S ?˜ Goals).
infer(S,[A|C], S,DC) :- (A :˜ D), append(D,C,DC). % ll
infer([A|S],[A|C], S,C). % scan
append([],L,L).
append([E|L],M,[E|N]) :- append(L,M,N).
(21) We can store the grammar in separate files, g1.pl and td.pl, and load them both:
1?-[td,g1].
td compiled, 0.00 sec, 1,116 bytes.
g1 compiled, 0.00 sec, 1,804 bytes.
Yes
2 ?- [the,idea,will,suffice] ?˜[ip].
Yes
3 ?- [the,idea,that,the,idea,will,suffice,will,suffice] ?˜[ip].
Yes
4 ?- [will,the,idea,suffice] ?˜[ip].
No
5?-halt.
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