Scope of decision-making: Amajor factor is the scale at which query processing and viewmaterialization decisions are made. At one extreme, all queries in the entire system are optimized together, using complete knowledge of the available materialized views, resources, and network bandwidth constraints — this poses all of the challenges of multi-query optimization plus a number of additional difficulties. In particular, work must be distributed globally across many peers, and decisions must be made about when and where to materialize results for future use. At the other end of the spectrum, every decision is made on a single-node, single-query basis — this is the familiar problem of.
