19 search results - page 2 / 4 » On Preservation under Homomorphisms and Unions of Conjunctiv... |
PODS
2004
ACM
14 years 7 months ago
2004
ACM
We study the problem of answering queries over sources with limited access patterns. Given a first-order query Q, the problem is to decide whether there is an equivalent query whi...
EDBT
2008
ACM
14 years 7 months ago
2008
ACM
Data exchange is the problem of transforming data structured under a schema (called source) into data structured under a different schema (called target). The emphasis of data exc...
WWW
2011
ACM
13 years 2 months ago
2011
ACM
The problem of answering SPARQL queries over virtual SPARQL views is commonly encountered in a number of settings, including while enforcing security policies to access RDF data, ...
EDBT
2008
ACM
14 years 7 months ago
2008
ACM
In this paper we study the problem of mining all frequent queries in a given database table, a problem known to be intractable even for conjunctive queries. We restrict our attent...
AMW
2009
13 years 8 months ago
2009
In data exchange, data are materialised from a source schema to a target schema, according to suitable source-to-target constraints. Constraints are also expressed on the target sc...