Principles of database and knowledge-base systems, Vol. I
Principles of database and knowledge-base systems, Vol. I
Decidable optimization problems for database logic programs
STOC '88 Proceedings of the twentieth annual ACM symposium on Theory of computing
Expressiveness of restricted recursive queries
STOC '89 Proceedings of the twenty-first annual ACM symposium on Theory of computing
On the first-order expressibility of recursive queries
PODS '89 Proceedings of the eighth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Logic programming and databases
Logic programming and databases
PODS '91 Proceedings of the tenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Graph rewriting: an algebraic and logic approach
Handbook of theoretical computer science (vol. B)
Expressive power of query languages
Theoretical studies in computer science
Undecidable optimization problems for database logic programs
Journal of the ACM (JACM)
Bounded arity Datalog ( ≠ ) queries on graphs
Journal of Computer and System Sciences - Special issue on principles of database systems
Conjunctive-query containment and constraint satisfaction
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Decidability and undecidability results for boundedness of linear recursive queries
Proceedings of the seventh ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
On the complexity of database queries
Journal of Computer and System Sciences
Achilles, Turtle, and Undecidable Boundedness Problems for Small DATALOG Programs
SIAM Journal on Computing
When is the evaluation of conjunctive queries tractable?
STOC '01 Proceedings of the thirty-third annual ACM symposium on Theory of computing
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Bounded-Arity Hierarchies in Fixed-Point Logics
CSL '93 Selected Papers from the 7th Workshop on Computer Science Logic
Recurrence with affine level mappings is p-time decidable for clp$({\mathbb r})$
Theory and Practice of Logic Programming
Undecidability and intractability results concerning datalog programs and their persistency numbers
ACM Transactions on Computational Logic (TOCL)
Efficient rule-based inferencing for OWL EL
IJCAI'11 Proceedings of the Twenty-Second international joint conference on Artificial Intelligence - Volume Volume Three
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The relation between Datalog programs and homomorphism problems and between Datalog programs and bounded treewidth structures has been recognized for some time and given much attention recently. Additionally, the essential role of persistent variables (of program expansions) in solving several relevant problems has also started to be observed. It turns out that to understand the contribution of these persistent variables to the difficulty of some expressibility problems, we need to understand the interrelationship among different notions of persistency numbers, some of which we introduce and/or formalize in the present work.This article is a first foundational study of the various persistency numbers and their interrelationships. To prove the relations among these persistency numbers, we had to develop some nontrivial technical tools that promise to help in proving other interesting results too. More precisely, we define the adorned dependency graph of a program, a useful tool for visualizing sets of persistent variables, and we define automata that recognize persistent sets in expansions.We start by elaborating on finer definitions of expansions and queries, which capture aspects of homomorphism problems on bounded treewidth structures. The main results of this article are (a) a program transformation technique, based on automata-theoretic tools, which manipulates persistent variables (leading, in certain cases, to programs of fewer persistent variables); (b) a categorization of the different roles of persistent variables; this is done by defining four notions of persistency numbers which capture the propagation of persistent variables from a syntactical level to a semantical one; (c) decidability results concerning the syntactical notions of persistency numbers that we have defined; and (d) the exhibition of new classes of programs for which boundedness is undecidable.