Optimization of Query Plans in the presence of Access Limitations

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 ord...

• Type: Conference
• Year: 2007
• Where: ICDT
• Authors: Andrea Calì, Diego Calvanese, Davide Martinenghi
• Keywords: Binding Patterns, Certain Binding Patterns, Database, ICDT 2007, Query Plan