Every logic program has a natural stratification and an iterated least fixed point model
PODS '89 Proceedings of the eighth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Arithmetic classification of perfect models of stratified programs
Fundamenta Informaticae
The well-founded semantics for general logic programs
Journal of the ACM (JACM)
Adding closed world assumptions to well-founded semantics
FGCS'921 Selected papers of the conference on Fifth generation computer systems
Reducing disjunctive to non-disjunctive semantics by shift-operations
Fundamenta Informaticae - Special issue: to the memory of Prof. Helena Rasiowa
The Semantics of Predicate Logic as a Programming Language
Journal of the ACM (JACM)
Tabling for non-monotonic programming
Annals of Mathematics and Artificial Intelligence
Smodels - An Implementation of the Stable Model and Well-Founded Semantics for Normal LP
LPNMR '97 Proceedings of the 4th International Conference on Logic Programming and Nonmonotonic Reasoning
Abduction in well-founded semantics and generalized stable models via tabled dual programs
Theory and Practice of Logic Programming
Revised stable models – a semantics for logic programs
EPIA'05 Proceedings of the 12th Portuguese conference on Progress in Artificial Intelligence
A Classification Theory Of Semantics Of Normal Logic Programs: Ii. Weak Properties
Fundamenta Informaticae
Layer Supported Models of Logic Programs
LPNMR '09 Proceedings of the 10th International Conference on Logic Programming and Nonmonotonic Reasoning
Design patterns for tabled logic programming
INAP'09 Proceedings of the 18th international conference on Applications of declarative programming and knowledge management
Stable model implementation of layer supported models by program transformation
INAP'09 Proceedings of the 18th international conference on Applications of declarative programming and knowledge management
Xsb: Extending prolog with tabled logic programming
Theory and Practice of Logic Programming - Prolog Systems
Goal-directed execution of answer set programs
Proceedings of the 14th symposium on Principles and practice of declarative programming
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For practical applications, the use of top-down query-driven proof-procedures is essential for an efficient use and computation of answers using Logic Programs as knowledge bases. Additionally, abductive reasoning on demand is intrinsically a top-down search method. A query-solving engine is thus highly desirable. The current standard 2-valued semantics for Normal Logic Programs (NLPs), the Stable Models (SMs) semantics, does not allow for top-down query-solving because it does not enjoy the relevance property -- and moreover, it does not guarantee the existence of a model for every NLP. To overcome these current limitations we introduce here a new 2-valued semantics for NLPs--the Layered Models semantics -- which conservatively extends the SMs, enjoys relevance and guarantees model existence among other useful properties. Moreover, for existential query answering there is no need to compute total models, but just the partial models that sustain the answer to the query, or one might simply know a model one exists without producing it; relevance ensures these can be extended to total models. A first implementation of a query-solving engine based on this new semantics is presented and described here. It uses the XSB-Prolog engine and its XASP interface to Smodels, thereby providing a useful tool built as a hybrid of the two systems and taking advantage of the best of each. Conclusions and further work end the paper.