Sustained Models and Sustained Answers in First-Order Databases.
Hendrik Decker, Juan Carlos Casamayor · UPCommons institutional repository (Universitat Politècnica de Catalunya) · 1993
First-order databases may contain clauses with disjunctive heads as well as deniais. We dis tinguish "sustained models" as alternatives of intended interpretations and show that they satisfy desirable properties. Extending Reiter's CWA, we define the "Sustained Worlds Assumption" and show that it also satisfies desirable properties. Roughly a positive answer is sustained if it is true in some sustained model. Queries without any positive sustained answer are non-monotonically but cautiously inferred to be false. We extend a procedure devised by Ross and Topor, for computing sustained answers. The extension comprises consistency checking and is shown to be sound and complete for finitary databases and queries.