Flexible and Scalable Query Planning in Distributed and Heterogeneous Environments

We present the application of the Planning by Rewriting (PbR) framework to query planning in distributed and heterogeneous environments. PbR is a new paradigm for e cient high-quality planning that exploits plan rewriting rules and e cient local search techniques to transform an easy-to-generate, but possibly suboptimal, initial plan into a high-quality plan. The resulting planner is scalable, exible, has anytime behavior, and, applied to query planning, yields a novel combination of traditional query optimization with heterogeneous information source selection. Query planners are the core component of mediator systems, which are becoming increasingly important in a world of interconnected information, and constitute excellent testbeds for planning technology.