On preservation under homomorphisms and unions of conjunctive queries.
Albert AtseriasAnuj DawarPhokion G. KolaitisPublished in: J. ACM (2006)
Keyphrases
- unions of conjunctive queries
- data exchange
- conjunctive queries
- query answering
- decision procedures
- transitive closure
- probabilistic databases
- relational queries
- data complexity
- answering queries
- dl lite
- relational algebra
- query evaluation
- data integration
- query containment
- schema mappings
- theorem proving
- integrity constraints
- query language
- data management
- modal logic
- np complete
- expressive power
- special case
- description logics
- query rewriting
- incomplete information
- reasoning tasks
- xml queries
- database queries
- relational database systems
- theorem prover
- computational complexity
- normal form