izmit, june 16, 2012 man-machine communication parsing and semantic analysis of natural language...

Izmit, June 16, 2012

Man-Machine CommunicationParsing and Semantic analysis of

Natural Language

Adam Mickiewicz University in PoznańDept of Computer Linguistics and Artificial Intelligence

[email protected]

Zygmunt Vetulani

Parsing and Semantic analysis of Natural Language


Formal Language

Terminal symbols : Polish (Turksh ?) wordsNon-terminal symbols : grammar category symbols (S, Sb, Ob,...)

Initial symbol : S

Context free rules (rewritting rules, production rules): ordered pairs <LS,RS>,

where LS is a single non-terminal symbol, RS is a finite sequence of terminal and/or non-terminal symbols

Notation : instead <LS,RS> we use to write LS RS

The re-writing operation consists in replacement od the non-terminal symbol LS by the sequence PS for some rule LS PS

Context free grammar is an arbitrary set of context-free rules



Derivation:P */G W : „W is the result of a finite iteration of the rewriting operations (first applied to P) on the basis of the context-free rewriting rules from G:

By the „language defined by the grammar G” we mean the following set L(G):

L(G) =df {W: for S being the initial symbol S */G W, where W is a sequence of terminal symbols}

IDEA: Consider Polish (Turkish etc.) as formal language (see Montague)

Computational PROBLEM : Find such a grammar that:

L(G) = the set of all correct sentences of Polish

(similar for Turkish, English, …)


For the CF grammars there exist effective parsing algorithms BUT some (rare) natural languages are not context-free.

(as e.g. one of the Swiss-German dialects (by Zürich), where constructions like NP1NP2NP3NP4NP5V1V2V3V4V5 are in use.

In (Gazdar & Mellish, 1989), p. 134, one can find an example (in English transcription) where the sentence with the meaning equivallent to

Claudia watched Helmut (who) let Eva to help Hans make Ulrike work

will have the surface form as follows

Claudia Helmut Eva Hans Ulrike watched let help make work.



An example of a CF grammar for a small fragment of Polish: a grammar for the sentence „Ala owns a nice cat” ("Ala ma ładnego kota") (and some other).

S Sb PredSb NGNG NameNG Adj NounNG NG Conective NGPred Verb NG

Verb "ma"Verb "miał"Verb "miała”.Name "Ala"Name "Olek"Adj "ładnego"Adj "złego"Noun "kota"Noun "psa"Connective "oraz " Connective ”i "



S stands for „sentence”Sb stands for „subject”NG stands for „noun group”Pred stands for „predication phrase”

DCG notation ( DCG – Definite Clause Grammar)

The DCG notation allows the usage of parameters in combination with the non-terminal and terminal symbols. These symbols must open special argument positions for parameters

Nonterminal symbols with parameters (arguments) are terms in which argument positions are occupied by these parameters (constants or variables).

Example : definition of a „sentence” in the DCG notation :

S Sb(Number,Number,nominative) Pred(Number,Gender)Pred(Number,Gender) Verb(Number,Gender) NG(_,_,accusative)...



Translating grammars to PROLOG

CF grammars may be „translated” to PROLOG using the method of difference lists

By difference list we mean a pair of two lists, the second of them is the n-th tail of the first one. Let (A,B) be a difference list. Then what remains from A after the substraction of B is called difference determined by (A,B).

For the non-terminal symbol K and the difference list (A,B) the predicate K(A,B) may be interpreted as follows:

”the category K is attributed to the difference determined by the difference list (A,B)”



The context free ruleC A B

may be interpreted as follows „the given list is of category C if its beginning is of the category A and the rest is of the category B”.

In terms of difference lists we may say it as follows : „if the difference (X0,X1) is of the category A, and the difference (X1,X2) is of the category B, then the difference (X0,X2) is of the category C".

This last statement is expressed in PROLOG as follows:

c(X0,X2) :- a(X0,X1), b(X1,X2).

The rule C A t B where t is a terminal symbol (or a sequence of terminal symbols) may be expressed in PROLOG as follows:

c(X0,X2) :- a(X0,[t|X1]), b(X1,X2).

The terminal rule C t is to be translated into PROLOG as:

c([t|X],X).



The CF ruleK t0 M0t1M1...tnMntn+1

where ti is a sequence of terminal symbols may be translated into PROLOGU as:

k([t0|X0],Xn+1) :- m0(X0,[t1|X1]) , m1(X1,[t2|X2]) , ... , mn(Xn,[tn+1|Xn+1])

The translation operation may be extended to context depending rules of the following form

Kt t0 M0t1M1...tnMntn+1

In this case the correct translation will be:k([t0|X0],[t|Xn+1]) :-

m0(X0,[t1|X1]) , m1(X1,[t2|X2]) , ... , mn(Xn,[tn+1|Xn+1])

(In this notation [t|X] stands for concatenation of the list t with the list X. )



Let us notice, that the following is a conditional statement about sequences of words in terms of relations (predicates) associating categories to difference lists. It is possible to generalise this formalisation considering category symbols as parameters denoting relations (rather then predicate symbols). For this purpose we introduce a general relation segment. We then translate

S Sb Pred into

segment(s,X0,X2) :- segment(sb,X0,X1),segment(pred,X1,X2).

We may of course impose further constraints on the composition of larger fragments from the smaller ones (as parts). E.g. the clause:

segment(s,X0,X2) :- segment(sb,L,R,X0,X1),segment(pred,L,R,X1,X2).

may be considered as the PROLOG translation of the CF-like parametrized rule

S Sb(L,R) Pred(L,R)



Conversion program (in PROLOG) of CF rules into PROLOG (according: Gazdar, Mellish, p. 114)

konwersja((LSwe->PSwe),(LSwy:-PSwy)) :- LSwy=..[LSwe,S0,SN], dodzmienne(PSwe,S0,SN,PSwy).dodzmienne((PSwe1,PSwe2),S0,SN,PSwy) :- !, dodzmienne(PSwe1,S0,S1,PSwy1), dodzmienne(PSwe2,S1,SN,PSwy2), kombinacja(PSwy1,PSwy2,PSwy).dodzmienne(PSwe,S0,SN,true) :- islist(PSwe),!, append(PSwe,SN,S0).dodzmienne(PSwe,S0,SN,PSwy) :- atom(PSwe), PSwy=..[PSwe,S0,SN].kombinacja(true,PSwy2,PSwy2):-!.kombinacja(PSwy1,true,PSwy1):-!.kombinacja(PSwy1,PSwy2,(PSwy1,PSwy2)).


islist([]).islist([_|_]).

% conversion of CF rules to Prologkonw_gram(G,P):-islist(G),konw_gram0(G,P).konw_gram0([],[]):-!.konw_gram0([R|G],[C|P]):-konwersja(R,C),konw_gram0(G,P).

% conversion with the tnstalation procedure (in PROLOG), where assertz_prog performs the asert of the translated clauses

install_gram(G):-konw_gram(G,P),assertz_prog(P).

assertz_prog(P):-islist(G),assertz_prog0(P).assertz_prog0([]):-!.assertz_prog0([C|P]):-assertz(C),assertz_prog0(P).

Notice: the above conversion procedure is simplified and the produced code may not behave correctly because of the „left-recursion” (it may need to be corrected manually)


Left-recursion solvingng(X0,X1) :- ng0(X0,X1).ng(X0,X1) :- ng1(X0,X1).ng0(X0,X1) :- name(X0,X1).ng0(X0,X1) :- noun(X0,X1).ng0(X0,X2):-

adj(X0,X1),noun(X1,X2).

ng0(X0,X2):- adj(X0,X1),name(X1,X2).

ng1(X0,X2):-ng0(X0,["oraz"|X1]),ng(X1,X2).

%left-recursion eliminatedpred(X0,X2):-

verb(X0,X1),ng(X1,X2).

%Conjunctionng1(X0,X3):-ng0(X0,X1]),connective(X1,X2),ng(X2,X3).

connective(["i"|X0],X0).connective(["oraz"|X0],X0).connective(["lub"|X0],X0).connective([","|X0],X0).


PROLOG translation of the grammar "Ala-ma-kota" into a PARSER

s(sentence(A,B),X0,X2) :- sb(A,X0,X1),pred(B,X1,X2).

pred(predicate_group(A,B),X0,X2):- verb(A,X0,X1), ng(B,X1,X2).

sb(subject(A),X0,X1) :- ng(A,X0,X1).ng(noun_gr_simple(A),X0,X1) :- ng0(A,X0,X1).ng(noun_gr_comp(A),X0,X1) :- ng1(A,X0,X1).ng0(name(A),X0,X1) :- name(A,X0,X1).ng0(noun(A),X0,X1) :- noun(A,X0,X1).ng0(adj_noun(A,B),X0,X2):-

adj(A,X0,X1), noun(B,X1,X2).ng0(adj_name(A,B),X0,X2):-

adj(A,X0,X1), name(B,X1,X2).ng1(noun_gr_con(A,B,C),X0,X3):-

ng0(A,X0,X1]), connective(B,X1,X2), ng(C,X2,X3).


verb(verb(['mieć',3,sing,_,present]),["ma"|X0],X0).verb(verb(['mieć',3,sing,masc.prze]),["miał"|X0],X0).verb(verb(['mieć',3,sing,fem,past]),["miała"|X0],X0).verb(verb(['kupić',3,sing,masc.prze]),["kupił"|X0],X0).verb(verb(['zobaczyć',3,sing,masc.prze]),["zobaczył"|X0],X0).verb(verb(['zobaczyć',3,sing,fem,past]),["zobaczyła"|X0],X0).adj(adjective(['ładny',nom,sing,fem]),["ładna"|X0],X0).adj(adjective(['ładny',gen,sing,fem]),["ładnej"|X0],X0).adj(adjective(['ładny',acc,sing,fem]),["ładną"|X0],X0).adj(adjective(['ładny',nom,sing,m]),["ładny"|X0],X0).adj(adjective(['ładny',gen,sing,m]),["ładnego"|X0],X0).adj(adjective(['ładny',acc,sing,m]),["ładnego"|X0],X0).adj(adjective(['zły',nom,sing,m]),["zły"|X0],X0).adj(adjective(['zły',nom,sing,fem]),["zła"|X0],X0).adj(adjective(['zły',gen,sing,m]),["złego"|X0],X0).adj(adjective(['zły',acc,sing,m]),["złego"|X0],X0).name(name(['Ala',nom,sing,fem]),["ala"|X0],X0).name(name(['Ala',nom,acc,fem]),["alę"|X0],X0).name(name(['Olek',nom,sing,m]),["olek"|X0],X0).name(name(['Olek',acc,sing,m]),["olka"|X0],X0).noun(noun(['kot',nom,sing,m]),["kot"|X0],X0).noun(noun(['kot',acc,sing,m]),["kota"|X0],X0).noun(noun(['pies',nom,sing,m]),["pies"|X0],X0).noun(noun(['pies',acc,sing,m]),["psa"|X0],X0).connective(connective(['i']),["i"|X0],X0).connective(connective(['oraz']),["oraz"|X0],X0).connective(connective(['lub']),["lub"|X0],X0).connective(connective(['przecinek']),[","|X0],X0). Izmit, June 12, 2014

Parsing of a sentence "Ala ma ładnego kota"

Prolog question:

?- s(T,['ala', 'ma', 'ładnego', 'kota'],[ ]).

Answer:T=sentence(subject(noun_gr_simple(name(['Ala',nom,sing,fem]))),predicate_group(verb(['mieć',3,sing,_,present]),noun_gr_simple(adj_noun(adjective(['ładny',gen,sing,m])),noun(['kot',acc,sing,m] )) ))

Notice: modification of a DCG resulted with a self-parsing grammar.



A self-parsing grammar may be extended to a semantic grammar through a modification of syntactic production rules with semantic evaluation procedures.The rule

structure(...) :- substructure_a(...), substructure_b(...).

will be transformed to

structure(..., Structure_meaning)):- substructure_a(...,Substructure_meaning_a), substructure_b(..., Substructure_meaning_b),semantics(Substructure_meaning_a, Substructure_meaning_b,

Structure_meaning).

‘semantics’ performs meaning composition

Example below: application to „Ala ma kota”



Assumption:

semantic representation of an affirmative sentence (=semantic content) provides information which support what the sentence tell us about the world („world”= database)

Remark:

Answering questions „czy...?” consists in application of a semantic procedure which calculates the semantic content of the affirmative text following the question word „czy” („whether”)


Semantic analysis in DCG

An example of a „world description” in PROLOG

owns(ala,kot1).owns(ala,kot2).owns(ola,kot1).owns(ola,pies1).

cats(kot1).cats(kot2).

dogs(pies1).

beatiful(kot1).



The Ala-ma-kota grammar with semantics

% semantics of an affirmative sentence reports on how the sentence is validated in the world

s(sentence(A,B),S,X0,X2) :- sb(A,S1,X0,X1),sb(B,S2,X1,X2),semantics(sentence,S1,S2,S).

go(predicate_group(A,B),S,X0,X2):- verb(A,S1,X0,X1), ng(B,S2,X1,X2), semantics(predicate_group,S1,S2,S).

sb(subject(A),S,X0,X1) :- ng(A,S,X0,X1).ng(noun_gr_simple(A),S,X0,X1) :- ng0(A,S,X0,X1).ng(noun_gr_comp(A),S,X0,X1) :- ng1(A,S,X0,X1).ng0(name(A),S,X0,X1) :- name(A,S1,X0,X1),semantics(name,S1,S).ng0(noun(A),S,X0,X1) :- noun(A,S1,X0,X1),semantics(rz,S1,S).ng0(adj_noun(adjective([F1|C]),noun([F2|C])),S,X0,X2):- adj(adjective([F1|C]),S1,X0,X1), noun(noun([F2|C]),S2,X1,X2),semantics(adj_noun,S1,S2,S).

ng0(adj_name(adjective([F1|C]),prop_name([F2|C])),S,X0,X2):- adj(adjective([F1|C]),S1,X0,X1), name(prop_name([F2|C]),S2,X1,X2),semantics(adj_name,S1,S2,S).

ng1(gr_noun_conn(A,B,C),S,X0,X3):-ng0(A,S1,X0,X1), connective(B,S2,X1,X2), ng(C,S3,X2,X3),semantics(noun_comp,S1,S2,S3,S).



Ala-ma-kota dictionaryverb(verb(['miecx',3,sing,_,present]),owns,['ma'|X0],X0).verb(verb(['miecx',3,sing,masc.prze]),owns,['mialx'|X0],X0).verb(verb(['miecx',3,sing,fem,past]),owns,['mialxa'|X0],X0).verb(verb(['miecx',3,mn,_,present]),owns,['majax'|X0],X0).przym(adjective(['lxadny',nom,sing,fem]),beatiful,['lxadna'|X0],X0).adj(adjective(['lxadny',gen,sing,fem]),beatiful,['lxadnej'|X0],X0).adj(adjective(['lxadny',acc,sing,fem]),beatiful,['zxadnax'|X0],X0).adj(adjective(['lxadny',nom,sing,m]),beatiful,['lxadny'|X0],X0).adj(adjective(['lxadny',gen,sing,m]),beatiful,['lxadnego'|X0],X0).adj(adjective(['lxadny',acc,sing,m]),beatiful,['lxadnego'|X0],X0).name(prop_name(['Ala',nom,sing,fem]),ala,[’Ala'|X0],X0).name(prop_name(['Ala',nom,acc,fem]),ala,[’Alex'|X0],X0).name(prop_name(['Ola',nom,sing,fem]),ola,[’Ola'|X0],X0).name(prop_name(['Ola',acc,sing,fem]),ola,[’Olex'|X0],X0).zaimek_pytajny(zaim_pyt([’kogo',acc,sing,m]),kogo,['kogo'|X0],X0).noun(noun(['kot',nom,sing,m]),cats,['kot'|X0],X0).noun(noun(['kot',acc,sing,m]),cats,['kota'|X0],X0).noun(noun(['pies',nom,sing,m]),dogs,['pies'|X0],X0).noun(noun(['pies',acc,sing,m]),dogs,['psa'|X0],X0).spojnik(connective(['i']),i,['i'|X0],X0).connective(connective(['oraz']),i,['oraz'|X0],X0).



Semantic and auxiliary procedures:semantics(adj_noun,S1,S2,S) :- ekstensja_konceptu(S1,E1),ekstensja_konceptu(S2,E2),przekroj(E2,E1,S).

semantics(name_z_prz,S1,S2,S) :- ekstensja_konceptu(S1,E1), ekstensja_nazwy(S2,E2),przekroj(E2,E1,S).

semantics(rz,S,E) :- ekstensja_konceptu(S,E).semantics(name,S,E) :- ekstensja_nazwy(S,E).semantics(noun_comp,S1,i,S3,S) :- suma_zbiorow(S1,S3,S).semantics(predicate_group,S1,S2,[S1,S2]).semantics(sentence,S1,[S2,S3],S):-lista_faktow(S2,S1,S3,S). semantics(sentence,[ala],[owns,[kot1,kot2]],S)ekstensja_konceptu(S,E):- T=..[S,X], setof(X,T,E). ekstensja_nazwy(S,[S]).lista_faktow(P,D1,D2,F) :-T=..[P,X,Y],setof(T,(nal-do(X,D1),nal-do(Y,D2),T), F).

lista_faktow(owns,[ala],[kot1,kot2],F)

suma_zbiorow(X,Y,Z) :- append(X,Y,Z0),bez_powtorzen(Z0,Z).nal-do(E,[E|_]).nal-do(E,[_|X]):-nal-do(E,X).



Example of a query:

?- s(X,Y,[‘Ala’,’i’,’Ola’,’mają’,’kota’],[ ]).

Answer:

X=sentence(subject(noun_gr_comp(gr_noun_connective(name(prop_name([‘Ala’,nom,sing,fem])),connective([i]),noun_gr_simple(name(name([‘Ola’,nom,sing,fem])))))),predicate_group(verb([miecx,3,mn,_0458,past]),noun_gr_simple(noun(noun([kot,acc,sing,m])))))

Y= [owns(ala,kot1),owns(ala,kot2),owns(ola,kot1)]



The 2-run analysis of a sentence.The first run (N=0) is non-deterministic, the second run (N=1) is deterministic, as it is controlled by the syntactic tree calculated at the first run (X).

?- s(0,X,_,[‘Ala’,’i’,’Ola’,’mają’,’kota’],[ ]), s(1,X,Y,[‘Ala’,’i’,’Ola’,’mają’,’kota’],[ ]).

Answer:

X=sentence(subject(noun_gr_comp(gr_noun_connective(name(prop_name([‘Ala’,nom,sing,fem])),connective([i]),noun_gr_simple(name(prop_name([‘Ola’,nom,sing,fem])))))),predicate_group(verb([miecx,3,mn,_0458,past]),noun_gr_simple(noun(noun([kot,acc,sing,m])))))

Y= [owns(ala,kot1),owns(ala,kot2),owns(ola,kot1)]



Semantic analysis in DCGTransformaction to a 2-runs grammar (addition of the variable N with values 0 or 1)

s(N,sentence(A,B),S,X0,X2) :- sb(N,A,S1,X0,X1),sb(N,B,S2,X1,X2),semantics(N,sentence,S1,S2,S).

question_about_subject(A,B),S,X0,X2) :- interrogative_subject_phrase(N,A,S1,X0,X1),sb(N,B,S2,X1,X2),semantics(N,pyt_o_podmiot,S1,S2,S).sb(N,predicate_group(A,B),S,X0,X2):- verb(A,S1,X0,X1), ng(B,S2,X1,X2), semantics(N,predicate_group,S1,S2,S).

sb(N,subject(A),S,X0,X1) :- ng(N,A,S,X0,X1).ng(N,noun_gr_simple(A),S,X0,X1) :- ng0(N,A,S,X0,X1).ng(N,noun_gr_comp(A),S,X0,X1) :- ng1(N,A,S,X0,X1).ng0(N,name(A),S,X0,X1) :- name(A,S1,X0,X1),semantics(N,name,S1,S).ng0(N,noun(A),S,X0,X1) :- noun(A,S1,X0,X1),semantics(N,rz,S1,S).ng0(N,adj_noun(adjective([F1|C]),noun([F2|C])),S,X0,X2):- adj(adjective([F1|C]),S1,X0,X1), noun(noun([F2|C]),S2,X1,X2),semantics(N,adj_noun,S1,S2,S).

ng0(N,adj_name(adjective([F1|C]),prop_name([F2|C])),S,X0,X2):- adj(adjective([F1|C]),S1,X0,X1), name(prop_name([F2|C]),S2,X1,X2),semantics(N,adj_name,S1,S2,S).

ng1(N,gr_noun_connective(A,B,C),S,X0,X3):-ng0(N,A,S1,X0,X1), connective(B,S2,X1,X2), ng(N,C,S3,X2,X3),semantics(N,noun_comp,S1,S2,S3,S).


Transformation of the semantic procedures:

semantics(0,_,_,_).semantics(0,_,_,_,_).semantics(0,_,_,_,_,_).

semantics(1,adj_noun,S1,S2,S) :- ekstensja_konceptu(S1,E1),ekstensja_konceptu(S2,E2),przekroj(E2,E1,S).

semantics(1,name_z_prz,S1,S2,S) :- ekstensja_konceptu(S1,E1), ekstensja_nazwy(S2,E2),przekroj(E2,E1,S).

semantics(1,rz,S,E) :- ekstensja_konceptu(S,E).semantics(1,name,S,E) :- ekstensja_nazwy(S,E).semantics(1,noun_comp,S1,i,S3,S) :- suma_zbiorow(S1,S3,S).semantics(1,predicate_group,S1,S2,[S1,S2]).semantics(1,sentence,S1,[S2,S3],S):-lista_faktow(S2,S1,S3,S).



Further exercices:

• take into account accord and government constraints within a sentence

• processing of ‘czy’-questions

• processing of questions about subject and complements


izmit, june 16, 2012 man-machine communication parsing and semantic analysis of natural language...

Documents

sequence of terminal

gender ng

s sb pred sb ng ng

grammar category symbols

words nonterminal symbols

free rules izmit

nonterminal symbol ls

grammar g