EDBT/ICDT 2009 Joint Conference

Electronic Conference Proceedings

• Welcome
• Full Program
• ICDT Sessions
  • Invited Talks
  • Research Track
    • Inconsistency and Repairs
    • Data Exchange
    • Data Structures and Algorithms
    • Uncertain Databases
    • XML
    • Querying
    • Business Processes
    • Streams, Data Mining, Complexity
    • Provenance
• ICDT Papers
• EDBT Sessions
• EDBT Papers
• Author Index
• Workshops

Querying Data Sources That Export Infinite Sets of Views

Authors

• Bogdan Cautis (TELECOM ParisTech - UMR CNRS 5141, France)
• Alin Deutsch (University of California San Diego, USA)
• Nicola Onose (University of California San Diego, USA)

Abstract

We study the problem of querying data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of queries. We revisit a classical setting in which the application queries are conjunctive queries and the source accepts families of (possibly parameterized) conjunctive queries specified as the expansions of a (potentially recursive) Datalog program with parameters. We say that query Q is expressible by the program P if it is equivalent to some expansion of P. Q is supported by P if it has an equivalent rewriting using some finite set of P's expansions. We present the first study of expressibility and support for sources that satisfy integrity constraints, which is generally the case in practice.

We identify practically relevant restrictions on the program specifying the views that ensure decidability under a mix of key and weakly acyclic foreign key constraints, and beyond. We show that these restrictions are as permissive as possible, since their slightest relaxation leads to undecidability. We present an algorithm that is guaranteed to be sound when applied to unrestricted input and in addition complete under the restrictions.

As a side-effect of our investigation, we settle two problems left open by prior work even while ignoring constraints. First, we improve the previously best known upper bound for deciding support in the constraint-free case, characterizing for the first time the problem's complexity. Second, we establish the precise relationship between expressibility and support: we show them to be inter-reducible in PTIME in both the absence and the presence of constraints. This enables us to employ the same algorithm for solving both problems.

Session

ICDT Research Session 2: Data Exchange (Monday, March 23, 14:00—15:30)