On conjunctive queries containing inequalities
Journal of the ACM (JACM)
Decidable optimization problems for database logic programs
STOC '88 Proceedings of the twentieth annual ACM symposium on Theory of computing
Containment of conjunctive queries: beyond relations as sets
ACM Transactions on Database Systems (TODS)
The complexity of querying indefinite data about linearly ordered domains
Journal of Computer and System Sciences - Special issue: dedicated to the memory of Paris Kanellakis
Complexity and expressive power of logic programming
ACM Computing Surveys (CSUR)
Datalog LITE: a deductive query language with linear time model checking
ACM Transactions on Computational Logic (TOCL)
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Theoretical Computer Science - Database theory
LICS '99 Proceedings of the 14th Annual IEEE Symposium on Logic in Computer Science
The complexity of relational query languages (Extended Abstract)
STOC '82 Proceedings of the fourteenth annual ACM symposium on Theory of computing
Monadic datalog and the expressive power of languages for Web information extraction
Journal of the ACM (JACM)
The Semijoin Algebra and the Guarded Fragment
Journal of Logic, Language and Information
Data exchange: semantics and query answering
Theoretical Computer Science - Database theory
The Nesting-Depth of Disjunctive μ-Calculus for Tree Languages and the Limitedness Problem
CSL '08 Proceedings of the 22nd international workshop on Computer Science Logic
Data exchange: On the complexity of answering queries with inequalities
Information Processing Letters
On rules with existential variables: Walking the decidability line
Artificial Intelligence
ICALP'11 Proceedings of the 38th international conference on Automata, languages and programming - Volume Part II
The limits of querying ontologies
ICDT'07 Proceedings of the 11th international conference on Database Theory
Finite satisfiability for guarded fixpoint logic
Information Processing Letters
Walking the complexity lines for generalized guarded existential rules
IJCAI'11 Proceedings of the Twenty-Second international joint conference on Artificial Intelligence - Volume Volume Two
Access patterns and integrity constraints revisited
Proceedings of the 16th International Conference on Database Theory
Ontology-based data access: a study through disjunctive datalog, CSP, and MMSNP
Proceedings of the 32nd symposium on Principles of database systems
The impact of disjunction on query answering under guarded-based existential rules
IJCAI'13 Proceedings of the Twenty-Third international joint conference on Artificial Intelligence
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A well-established and fundamental insight in database theory is that negation (also known as complementation) tends to make queries difficult to process and difficult to reason about. Many basic problems are decidable and admit practical algorithms in the case of unions of conjunctive queries, but become difficult or even undecidable when queries are allowed to contain negation. Inspired by recent results in finite model theory, we consider a restricted form of negation, guarded negation. We introduce a fragment of SQL, called GN-SQL, as well as a fragment of Datalog with stratified negation, called GN-Datalog, that allow only guarded negation, and we show that these query languages are computationally well behaved, in terms of testing query containment, query evaluation, open-world query answering, and boundedness. GN-SQL and GN-Datalog subsume a number of well known query languages and constraint languages, such as unions of conjunctive queries, monadic Datalog, and frontier-guarded tgds. In addition, an analysis of standard benchmark workloads shows that many uses of negation in SQL in practice are guarded.