OptimAX: optimizing distributed continuous queries

National audienceThe system we propose to present, OptiMAX, applies the principles of distributed query optimization to the problem of distributed evaluation of continuous XML queries. OptiMAX is an optimizer for Active XML documents (AXML in short). It is implemented as a module which can be used next to an AXML peer, and it may be invoked whenever users ask queries on their AXML documents. The optimizer draws up an initial query plan, and then attempts to rewrtite it using a combination of heuristics and cost information in order to improve the plan's performance estimates. An interesting feature is that all plans are AXML documents themselves. When the optimizer has retained a plan, it hands it to the AXML peer, which evaluates it directly following the decisions taken by the optimizer