The first implementation of the query pack execution algorithm is the meta-interpreter meta_execute_qp(Q). The meta-interpreter uses the following labelling in its representation of a query pack:
Consider the query pack a, (b, (c or d or e) or f or g, (h or i or j)). Note that the atoms in the example could in general be arbitrary conjunctions of non-ground terms. Its labelling is shown in Figure 3.
A labelled query pack is then represented as a Prolog term as follows (with the father of ):
The example of Figure 3 has the following representation (as a Prolog term):
(a, or([(b,or([(c,leaf(2,1,1)),(d,leaf(2,2,2)),(e,leaf(2,3,3))],1,2,1,3)), (f,leaf(1,2,4)), (g,or([(h,leaf(3,1,5)),(i,leaf(3,2,6)),(j,leaf(3,3,7))],1,3,3,3))], 0,1,1,3))
During the execution of the meta-interpreter, solved/2 facts are asserted. Each fact solved(, ) denotes that the child with number from query pack with number has succeeded. Such facts are asserted when reaching a leaf and also when all children of a query pack have succeeded. The meta-interpreter only executes children for which no solved/2 fact has been asserted.
Note that the time-complexity of this meta-interpreter is not yet as desired. Execution of a query pack will always be dependent on the number of original children, instead of the number of remaining (as yet unsuccessful) children.
run_QueryPack(Q) :- preprocess(Q, Qlabeled, 0, 1, 1, 1, _, _), % The code for preprocessing is given in Appendix A retractall(solved(_, _)), meta_execute_qp(Qlabeled), solved(0, _), !. meta_execute_qp((A,B)) :- !, call(A), meta_execute_qp(B). meta_execute_qp(or(Cs, QpNbF, QpNb, ChildNb, TotCs)) :- !, % 'or' corresponds to a non-leaf query pack handlechildren(Cs, QpNb, 1), all_solved(QpNb, 0, TotCs), assert(solved(QpNbF,ChildNb)). meta_execute_qp(leaf(QpNbF, ChildNb , QueryNb)) :- !, % 'leaf' corresponds to the end of a query write(succeed(QueryNb)), nl, assert(solved(QpNbF,ChildNb)). handlechildren(, _, _). handlechildren([C|_], QpNb, ChildNb) :- not(solved(QpNb,ChildNb)), once(meta_execute_qp(C)), fail. handlechildren([_|Cs], QpNb, ChildNb) :- ChildNb1 is ChildNb + 1, handlechildren(Cs, QpNb, ChildNb1). all_solved(QpNb, ChildNb, TotCs) :- (ChildNb = TotCs -> true ; ChildNb1 is ChildNb + 1, solved(QpNb, ChildNb1), all_solved(QpNb, ChildNb1, TotCs) ).