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Bounds in the propagation of selection into logic programs. (English) Zbl 0796.68054

Summary: We consider the problem of propagating selections into logic programs (i.e., recursive Horn clause programs). In particular, we study the class of chain programs and formalize selection propagation on such a logic programs as: the task of finding an equivalent program containing only monadic derived predicates. Selection propagation is always possible for database programs (i.e., first-order formula programs) and is often a desirable optimization. We show that the situation is qualitatively different for logic programs. We associate a context-free language \(L(H)\) with every chain program \(H\). We show that, given \(H\), propagating a selection involving some constant is possible iff \(L(H)\) is regular and therefore undecidable. We also show that propagating a selection of the form \(p(X,X)\) is possible iff \(L(H)\) is finite and therefore decidable. We demonstrate the connection of these two cases, respectively, with the weak monadic second-order theory of one successor and with monadic generalized spectra. We further clarify the analogy between chain programs and context-free languages from the point of view of program equivalence, first-order expressibility over finite structures, and selection propagation heuristics.

MSC:

68N17 Logic programming
68P15 Database theory
68Q45 Formal languages and automata
68N01 General topics in the theory of software
Full Text: DOI

References:

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