Natural Language Processing1. A few problems from your work2. ‘append’ program - two lists to one or split
one list into two3. How to write a parser in Prolog, how it
works (ref. Paul’s book, page 78-85)4. Construct parse trees5. Use of parse trees
Common Problems/Mistakes
• % an empty set is a subset of any set Lsubset([], [L]). % what is wrong?
• When call ‘not_u_turn’, must make sure that both parameters are not variables.not_u_turn(X,Y):- \+(u_turn(X,Y).
3
(re-used slide) Manipulating Lists Ex. 5 – Appending 2 lists
Write a program append(L1,L2,L3) where L3 is the concatenation of L1 and L2.e.g. append([1,2], [a,b,c],L) returns L = [1,2,a,b,c]Q: how about append(L1, L2, [1,2,3]) ?append([],L,L).append([X|T1],T2,[X|T3]):-
append(T1,T2,T3).(in SICStus Prolog, append is a builtin)
How many different way ‘append’ program can be called?
• append([a], [student], [a,student]). % in/in/in• append([you,are],[in,’2q49’], L). % in/in/out
L = [you,are,in,’2q49’]• append([you], L, [you,are,a,student]). % in/out/in
L = [are,a,student]• append(L, [student], [i,am,a,student]). % out/in/in
L = [i,am,a]• append([you],L1,L2). % in/out/out
• append(L1,[you],L2). % out/in/out
• append(L1,L2,[i,am,a,student]). % out/out/in
One port can be either Input or output
append
Parsing – work out the structure of a sentence The first step toward to processing
language
• I like uwe very much
subject verb object_phrase
noun_phrase adverb
I like uwe very much
Why do we need parser?
Traditional Parser’s Role:• Check if a sentence syntactically correct• If yes, construct a parse tree for the
sentence
Non-traditional Role:• Generate possible sentences
Why do we need parse tree?• Help us to understand the meaning of a
sentence• Allow us to transform a sentence to other
forms: Machine translation.
e.g. ‘I like uwe’ in Japanese, the order is ‘I uwe like’. We need to know both structures in order to translate
Reconstructing a new sentence from an old one.e.g. ‘I like uwe’ can be changed to ‘why do you like uwe’. This is useful for creating a conversation for chatbot.
A Small ExampleLet’s use this small set
of vocabulary { i, you, me, us, uwe,
cs_course, robolics_course, like, love, very_much }
Next, we define a verybasic English grammarshown in the left box.
sentence --> subject_phrase, verb, object_phrase.
subject_phrase --> subject_pronoun.
object_phrase --> object_pronoun, adverb.
object_phrase --> noun_phrase, adverb.
noun_phrase --> determiner, noun.
‘-->’ means ‘defined as’ and ‘consists of’
A Small Example (cont)
subject_pronoun --> [i].subject_pronoun --> [we].subject_pronoun --> [you].
object_pronoun --> [you].object_pronoun --> [me].object_pronoun --> [us].
determiner --> [].% determiner --> [a].% determiner --> [the].
noun --> [uwe].noun --> [cs_course].noun --> [robotics_course].
adverb --> [very, much].adverb --> [].
verb --> [like].verb --> [love].
How to write it in Prolog?• Those (in slide 9-10) are already Prolog code !• ‘-->’ is specially added for writing a parser
sentence --> subject_phrase, verb, object_phrase.
is equivalent to sentence(L1,Rest):- subject_phrase(L1,L2),
verb(L2,L3), object_phrase(L3,Rest).
So, we can call ‘sentence([we,love,uwe],[]).’ to check if it it a legal sentence
Having those defined, we can do lots of things:
| ?- sentence([we, love, uwe],[]).yes
| ?- sentence([love,you],[]).no
| ?- sentence([we, like, you, because], R).R = [because] ? yes
| ?- sentence(L,[]).L = [i,like,uwe,very,much] ? ;L = [i,like,uwe] ? ;L = [i,like,cs_course,very,much] ? ;L = [i,like,cs_course] ? ;
L = [i,like,robotics_course,very,much] ? ;L = [i,like,robotics_course] ? ;L = [i,like,you,very,much] ? ;L = [i,like,you] ? ;L = [i,like,me,very,much] ? ;L = [i,like,me] ? ;L = [i,like,us,very,much] ? yes
| ?- findall(L, sentence(L,[]), All).All = [[i,like,uwe,very,much],[i,like,uwe],
[i,like,cs_course,very,much],[i,like,cs_course],[i,like,robotics_course,very,much],[i,like,robotics_course],[i,like,you,very|...],[i,like,you],[i,like|...],[...|...]|...] ?
What is a legal sentence?
Generate all legal sentences!
Check if it a legal sentence
In order to generate parse tree we need to change the code (version 2)
New Oldsentence(s(X, Y, Z)) -->
subject_phrase(X), verb(Y), object_phrase(Z).
subject_phrase(sp(X)) --> subject_pronoun(X).
object_phrase(op(X,Y)) --> noun_phrase(X), adverb(Y).
object_phrase(op(X, Y)) --> object_pronoun(X), adverb(Y).
noun_phrase(np(Y)) --> noun(Y).
prepositional_phrase(pp(X, Y)) --> preposition(X), place_name(Y).
sentence --> subject_phrase, verb, object_phrase.
subject_phrase --> subject_pronoun.
object_phrase --> noun_phrase, adverb.
object_phrase --> object_pronoun, adverb.
noun_phrase --> noun.
prepositional_phrase --> preposition, place_name.
In order to generate parse tree we need to change the code (version 2)
New Oldpreposition(prep(in)) --> [in].preposition(prep(at)) --> [at].preposition(prep(from)) --> [from].
place_name(pname(reception)) --> [reception].
place_name(pname(london)) --> [london].place_name(pname(bristol)) --> [bristol].place_name(pname(X)) -->
[X], { next(X,_,_,_,_) }.
subject_pronoun(spn(i)) --> [i].subject_pronoun(spn(we)) --> [we].subject_pronoun(spn(you)) --> [you].
object_pronoun(opn(you))--> [you].object_pronoun(opn(me))--> [me].object_pronoun(opn(us))--> [us]. %...
preposition --> [in].preposition --> [at].preposition --> [from].
place_name --> [reception].place_name --> [london].place_name --> [bristol].place_name -->
[X], { next(X,_,_,_,_) }.
subject_pronoun --> [i].subject_pronoun --> [we].subject_pronoun --> [you].
object_pronoun --> [you].object_pronoun --> [me].object_pronoun --> [us]. % ………
Test on version 2 – a list of words to a parse tree| ?- sentence(Tree, [i,love,you],[]).Tree = s(sp(spn(i)),vd(love),op(opn(you),ad([]))) ? ;
| ?- sentence(Tree, [i,love,you,very,much],[]).Tree = s(sp(spn(i)),vd(love),op(opn(you),ad([very,much]))) ? yes
| ?- sentence(T,[i,am,in,bristol],[]).T = s(s_2b([i,am]),pp(prep(in),pname(bristol))) ?
| ?- sentence(s(sp(spn(i)),vd(love),op(opn(you),ad([very,much]))), L,K).L = [i,love,you,very,much|K] ? yes% 6| ?- sentence(s(s_2b([i,am]),pp(prep(in),pname(bristol))), L,[]).L = [i,am,in,bristol] ?
Test on version 2 – a parse tree to a list of word
Add a few more grammar rules for questions
question(q(why,do,S)) --> [why, do], sentence(S).question(q(do,S)) --> [do], sentence(S).
/* after added the above line, we can handle questions like: */| ?- question(Tree, [why,do ,you, love,me],[]).Tree =
q(why,do,s(sp(spn(you)),vd(love),op(opn(me),ad([])))) ?| ?- question(Tree, [do ,you, like,uwe],[]).Tree = q(do,s(sp(spn(you)),vd(like),op(np(uwe),ad([])))) ?
How to change a sentence to a question beginning with ‘why’?
I like uwe Why do you like uwe
mapping(s2why, %
s(sp(spn(N1)), vd(V), op(np(noun(N2)), ad(X))),
q(why,do,s(sp(spn(P1)),vd(V),op(np(noun(N2)),ad(X)))) ) :- mapping_spn(N1, P1).
How to change a sentence to a question beginning with ‘why’?
I like you Why do you like me
mapping(s2why, % type of mapping
s(sp(spn(N1)),vd(V),op(opn(N2),ad(X))),
q(why,do,s(sp(spn(P1)),vd(V),op(opn(P2),ad(X)))) ) :- mapping_spn(N1, P1), mapping_opn(N2, P2).
Parser Parser converging parse trees
| ?- question(Tree, [why,do,you,love,me],[]), mapping(s2why, T, Tree), sentence(T, L, []).L = [i,love,you],
T = s(sp(spn(i)),vd(love),op(opn(you),ad([]))),
Tree = q(why,do,s(sp(spn(you)),vd(love),op(opn(me),ad([])))) ?
| ?- sentence(T1, [i,like,uwe],[]), mapping(s2why,T1,T2), question(T2, L,[]).L = [why,do,you,like,uwe],T1 = s(sp(spn(i)),vd(like),op(np(noun(uwe)),ad([]))),T2 = q(why,do,s(sp(spn(you)),vd(like),op(np(noun(uwe)),ad([])))) ? yes% 7
Put them together (file english.pl)
test:- repeat, readin(S), gen_reply(S,Ans), write_list(Ans), nl, S = [bye|_].
test:- write(bye),nl.
gen_reply(S,Reply):- sentence(Tree1, S, _Rest),!, mapping(s2why,Tree1, Tree2),question(Tree2, Rep,[]),append(Rep, ['?'], Reply).
gen_reply(S,Reply):- question(Tree2, S, _Rest),!, mapping(s2q,Tree1, Tree2),sentence(Tree1, Rep,[]),append([yes, ','|Rep], ['!'], Reply).
gen_reply([bye|_],[bye ,for, now, '.']).
gen_reply(_,[what,'?']). % default case
% ‘!’ will be explained in next week
A test example from this simple chatbot
| ?- test.|: hi!|: what ?
Hi!|: what ?
i love you!|: why do you love me ?
don't know.|: what ?
do you love me?|: yes , i love you !
bye.bye for now .
