Graduate Thesis Or Dissertation
 

Disjunctions in forward chaining logic programming

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9z903227h

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  • A forward-chaining logic programming system (FORLOG) has been developed at Oregon State University. This system coupled with an assumption-based truth maintenance system (ATMS), provides an alternative to the logic programming paradigm of backward-chaining with Horn clauses. To compare FORLOG to this paradigm, we define a subset of FORLOG, called mini-FORLOG, with a restricted syntax. This syntax is derived in a straight forward manner from a Horn clause program. We prove that mini-FORLOG is procedurally isomorphic to Horn clause programming. Logic programs derived from Horn clause programs contain implications with disjunctive consequences. Each disjunct may either lead to a solution or to a contradiction. We want FORLOG to choose only those that lead to solutions. In an attempt to remove the nondeterminism inherent in this choice, FORLOG compiles implications into several simpler ones, all void of disjunctions. Even with compilation, FORLOG often must pursue each nondeterministic choice, some of which may turn out to be contradictory. This requires FORLOG to handle discovered inconsistencies. With traditional logic, the existence of an inconsistency invalidates all deductions made. FORLOG uses the ATMS to maintain consistency of its database of facts. One alternative in a disjunction might not terminate. It turns out that FORLOG can use contradictions discovered during computation to avoid some of these cases. This process involves resolving the disjunctions with discovered contradictions.
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