Optimization of Query Plans in the Presence of Access Limitations

Andrea Calì, Diego Calvanese, and Davide Martinenghi

Proc. of the ICDT 2007 Workshop on Emerging Research Opportunities in Web Data Management (EROW 2007). Volume 229 of CEUR Workshop Proceedings, http://ceur-ws.org/. 2007.

We consider the problem of querying data sources that have limited capabilities and can thus only be accessed by complying with certain binding patterns for their attributes. This is often the case, e.g., in the context of data on the web queryable via web forms as well as in legacy data wrapped in relational tables. In such contexts, computing the answer to a user query cannot be done as in a traditional database; instead, a query plan is needed that takes the access limitations into account. In this paper, we develop a technique for producing a (possibly recursive) Datalog program that retrieves all obtainable answers for a query with limited source capabilities. In particular, we improve with respect to a previously published algorithm for optimizing query answering for conjunctive queries. Furthermore, we extend it to the context of unions of conjunctive queries. The algorithm exploits the structure of the query together with the binding patterns present in the source schema in order to compute an optimized query plan. The optimization excludes from the query plan the sources that are not relevant for the answer thus reducing the number of accesses to the sources.


@inproceedings{EROW-2007,
  title = "Optimization of Query Plans in the Presence of Access Limitations",
   year = "2007",
   author = "Andrea Calì and Diego Calvanese and Davide
Martinenghi",
   booktitle = "Proc. of the ICDT 2007 Workshop on Emerging Research
Opportunities in Web Data Management (EROW 2007)",
   volume = "229",
   series = "CEUR Workshop Proceedings, http://ceur-ws.org/",
}
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