Optimizing Large Join Queries in Mediation Systems

In data integration systems, queries posed to a mediator need to be translated into a sequence of queries to the underlying data sources. In a heterogeneous environment, with sources of diverse and limited query capabilities, not all the translations are feasible. In this paper, we study the problem of nding feasible and e cient query plans for mediator systems. We consider conjunctive queries on mediators and model the source capabilities through attribute-binding adornments. We use a simple cost model that focuses on the major costs in mediation systems, those involved with sending queries to sources and getting answers back. Under this metric, we develop two algorithms for source query sequencing one based on a simple greedy strategy and another based on a partitioning scheme. The rst algorithm produces optimal plans in some scenarios, and we show a linear bound on its worst case performance when it misses optimal plans. The second algorithm generates optimal plans in more scenario...

• Type: Conference
• Year: 1999
• Where: ICDT
• Authors: Ramana Yerneni, Chen Li, Jeffrey D. Ullman, Hector Garcia-Molina
• Keywords: Cient Query Plans, Database, ICDT 1999, Limited Query Capabilities, Optimal Plans