An access cost-aware approach for object retrieval over multiple sources

Source and object selection and retrieval from large multi-source data sets are fundamental operations in many applications. In this paper, we initiate research on efficient source (e.g., database) and object selection algorithms on large multi-source data sets. Specifically, in order to acquire a specified number of satisfying objects with minimum cost over multiple databases, the query engine needs to determine the access overhead for individual data sources, the overhead of retrieving objects from each source, and possibly other statistics such as estimating the frequency of finding a satisfying object in order to determine how many objects to retrieve from each data source. We adopt a probabilistic approach to source selection utilizing a cost structure and a dynamic programming model for computing the optimal number of objects to retrieve from each data source. Such a structure can be a valuable asset where there is a monetary or time related cost associated with accessing large distributed databases. We present a thorough experimental evaluation to validate our techniques using real-world data sets.