19 search results - page 2 / 4 » On Preservation under Homomorphisms and Unions of Conjunctiv... |
PODS
2004
ACM
14 years 5 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 5 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
12 years 11 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 5 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 6 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...