19 search results - page 1 / 4 » On Preservation under Homomorphisms and Unions of Conjunctiv... |
PODS
2004
ACM
14 years 4 months ago
2004
ACM
Unions of conjunctive queries, also known as select-project-join-union queries, are the most frequently asked queries in relational database systems. These queries are definable b...
EDBT
2004
ACM
14 years 4 months ago
2004
ACM
We study the problem of answering queries over sources with limited access patterns. The problem is to decide whether a given query Q is feasible, i.e., equivalent to an executable...
ICDT
2009
ACM
14 years 5 months ago
2009
ACM
We study containment and equivalence of (unions of) conjunctive queries on relations annotated with elements of a commutative semiring. Such relations and the semantics of positiv...
FOCS
2003
IEEE
13 years 9 months ago
2003
IEEE
We give a complexity theoretic classification of homomorphism problems for graphs and, more generally, relational structures obtained by restricting the left hand side structure ...
AMAI
2007
Springer
13 years 4 months ago
2007
Springer
We present here a formal foundation for an iterative and incremental approach to constructing and evaluating preference queries. Our main focus is query modification: a query tran...