Efficient evaluation of queries in a mediator for WebSources

  • Authors:

  • Vladimir Zadorozhny;Louiqa Raschid;Maria Esther Vidal;Tolga Urhan;Laura Bright

  • Affiliations:

  • University of Pittsburgh, Pittsburgh, PA;University of Maryland, College Park, MD;Simon Bolivar University, Caracas, Venezuela;BEA Systems, Inc., San Jose, CA;University of Maryland, College Park, MD

  • Venue:
  • Proceedings of the 2002 ACM SIGMOD international conference on Management of data
  • Year:
  • 2002

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Abstract

We consider an architecture of mediators and wrappers for Internet accessible WebSources of limited query capability. Each call to a source is a WebSource Implementation (WSI) and it is associated with both a capability and (a possibly dynamic) cost. The multiplicity of WSIs with varying costs and capabilities increases the complexity of a traditional optimizer that must assign WSIs for each remote relation in the query while generating an (optimal) plan. We present a two-phase Web Query Optimizer (WQO). In a pre-optimization phase, the WQO selects one or more WSIs for a pre-plan; a pre-plan represents a space of query evaluation plans (plans) based on this choice of WSIs. The WQO uses cost-based heuristics to evaluate the choice of WSI assignment in the pre-plan and to choose a good pre-plan. The WQO uses the pre-plan to drive the extended relational optimizer to obtain the best plan for a pre-plan. A prototype of the WQO has been developed. We compare the effectiveness of the WQO, i.e., its ability to efficiently search a large space of plans and obtain a low cost plan, in comparison to a traditional optimizer. We also validate the cost-based heuristics by experimental evaluation of queries in the noisy Internet environment.