The simplest version of ask prompts the user with the requested attribute and value and seeks confirmation or denial of the proposed information.
Source: Building Expert Systems in PROLOG Publisher
Program source code: interface.pl
ask(Attr, Val):- write(Attr:Val), write('? '), read(yes). eats(X):- ask(eats, X). feet(X):- ask(feet, X). wings(X):- ask(wings, X). neck(X):- ask(neck, X). color(X):- ask(color, X).