How to do a Tree Transfer in prolog for MT

Question

I need to find a way to Transfer a parse tree in to another with different order. It is for machine translation project with two languages with SVO and SOV architecture.

t1 = s(np(n(he)), vp( v(went), np(n(home))))

and I want it to be

t2 = s(np(n(he)), vp( np(n(home)), v(went)))

according to a rule that represent t1 represent the SVO language and t2 represent the SOV language architecture.

And the rule set should be applicable for complex sentences with adjectives and adverbs.

t1 = s(np(n(he)), vp( v(went), np(adj(his), n(home))))

t2 = s(np(n(he)), vp( np(adj(his), n(home)), v(went)))

Any comment would be useful

thanks Mathee

Answer 1

the easier way it's the declaration of any transformation to be done, via pattern matching, and a generic rule working recursively on any pattern:

% specialize for VP
transfer(vp(X,Y), vp(V,U)) :- !,
    transfer(X,U), transfer(Y,V).

% generic rule, work out arguments
transfer(X, Y) :-
    X =.. [F|Xs],
    maplist(transfer, Xs, Ys),
    Y =.. [F|Ys].

If you need your program to be able to work bidirectionally, check the variables instantiation in generic rule

transfer(X, Y) :-
    nonvar(X), !, X =.. [F|Xs],
    maplist(transfer, Xs, Ys),
    Y =.. [F|Ys].
transfer(X, Y) :-
    Y =.. [F|Ys],
    maplist(transfer, Xs, Ys),
    X =.. [F|Xs].

yields (for instance)

?- transfer(s(np(n(he)), vp( v(went), np(adj(his), n(home)))),T2).
T2 = s(np(n(he)), vp(np(adj(his), n(home)), v(went))).

?- transfer(T1,$T2).
T1 = s(np(n(he)), vp(v(went), np(adj(his), n(home)))).