Adapting to bandwidth variations in wide-area data combination

Efficient data combination over wide-area networks is hard as these networks have large variations in available bandwidth. We examine the utility of changing the location of combination operations as a technique to adapt to variations in network bandwidth. We try to answer the following questions. First, does relocation of operators provide a significant performance improvement? Second, is on-line relocation useful or does a one-time positioning at start-up time provide most if not all the benefits? If on-line relocation is useful, how frequently should it be done and is global knowledge of network performance required or can local knowledge and local relocation of operators sufficient? Fourth, does the effectiveness of operator relocation depend on the ordering of the combination operations. That is, are certain ways of ordering more amenable to adaptation than others? Finally, how do the results change as the number of data sources changes?