A natural approach to implementing such systems is to use an existing query-based data collection system for sen- sor networks. Through queries, a user can ask for the data he or she is interested in without concern for the technical details of how that data will be retrieved or processed. A number of research projects, including Cougar [31], Di- rected Diffusion [12], and TinyDB [19,20] have advocated a query-based interface to sensornets, and several imple- mentations of query systems have been built and deployed. Unfortunately, these existing query systems do not pro- vide an efficient way to evaluate.
