Incomplete Information in Relational Databases
Journal of the ACM (JACM)
On the integrity of databases with incomplete information
PODS '86 Proceedings of the fifth ACM SIGACT-SIGMOD symposium on Principles of database systems
Journal of the ACM (JACM)
On the representation and querying of sets of possible worlds
Selected papers of the workshop on Deductive database theory
Semantics of types for database objects
Theoretical Computer Science
Using powerdomains to generalize relational databases
Theoretical Computer Science
Semantics of programming languages: structures and techniques
Semantics of programming languages: structures and techniques
Equality and Domain Closure in First-Order Databases
Journal of the ACM (JACM)
Data integration: a theoretical perspective
Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
A Semantics-based Approach to Design of Query Languages for Partial Information
Selected Papers from a Workshop on Semantics in Databases
On Indefinite Databases and the Closed World Assumption
Proceedings of the 6th Conference on Automated Deduction
On the decidability and complexity of query answering over inconsistent and incomplete databases
Proceedings of the twenty-second ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
LICS '95 Proceedings of the 10th Annual IEEE Symposium on Logic in Computer Science
Data exchange: getting to the core
ACM Transactions on Database Systems (TODS) - Special Issue: SIGMOD/PODS 2003
On preservation under homomorphisms and unions of conjunctive queries
Journal of the ACM (JACM)
Representing and querying XML with incomplete information
ACM Transactions on Database Systems (TODS)
Homomorphism preservation theorems
Journal of the ACM (JACM)
XML with incomplete information
Journal of the ACM (JACM)
Relational and XML Data Exchange
Relational and XML Data Exchange
Data exchange beyond complete data
Proceedings of the thirtieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Incomplete information and certain answers in general data models
Proceedings of the thirtieth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
On the complexity of query answering over incomplete XML documents
Proceedings of the 15th International Conference on Database Theory
Hi-index | 0.00 |
The term naive evaluation refers to evaluating queries over incomplete databases as if nulls were usual data values, i.e., to using the standard database query evaluation engine. Since the semantics of query answering over incomplete databases is that of certain answers, we would like to know when naive evaluation computes them: i.e., when certain answers can be found without inventing new specialized algorithms. For relational databases it is well known that unions of conjunctive queries possess this desirable property, and results on preservation of formulae under homomorphisms tell us that within relational calculus, this class cannot be extended under the open-world assumption. Our goal here is twofold. First, we develop a general framework that allows us to determine, for a given semantics of incompleteness, classes of queries for which naive evaluation computes certain answers. Second, we apply this approach to a variety of semantics, showing that for many classes of queries beyond unions of conjunctive queries, naive evaluation makes perfect sense under assumptions different from open-world. Our key observations are: (1) naive evaluation is equivalent to monotonicity of queries with respect to a semantics-induced ordering, and (2) for most reasonable semantics, such monotonicity is captured by preservation under various types of homomorphisms. Using these results we find classes of queries for which naive evaluation works, e.g., positive first-order formulae for the closed-world semantics. Even more, we introduce a general relation-based framework for defining semantics of incompleteness, show how it can be used to capture many known semantics and to introduce new ones, and describe classes of first-order queries for which naive evaluation works under such semantics.