natural language processing 1.a few problems from your work 2.‘append’ program - two lists to...

Natural Language Processing

1. A few problems from your work

2. ‘append’ program - two lists to one or split one list into two

3. How to write a parser in Prolog, how it works (ref. Paul’s book, page 78-85)

4. Construct parse trees

5. Use of parse trees

Common Problems/Mistakes

• % an empty set is a subset of any set L

subset([], [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 Example

Let’s use this small set of vocabulary

{ i, you, me, us, uwe, cs_course, robolics_course, like, love, very_much }

Next, we define a very

basic English grammar

shown 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 Old

preposition(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

natural language processing 1.a few problems from your work 2.‘append’ program - two lists to...

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