Loosely-specified query processing in large-scale information systems

Challenging issues for processing queries specified over large-scale information spaces (for example, Digital Libraries or the World Wide Web) include the diversity of the information sources in terms of their structures, query interfaces and search capabilities, as well as the dynamics of sources continuously being added, removed or upgraded. In this paper, we give an innovative solution for query planning in such environments. The foundation of our solution is the Dynamic Information Integration Model (DIIM) which supports the specification of not only content but also capabilities of resources without requiring the establishment of a uniform integration schema. Besides the development of the DIIM model, contributions of this paper include: (1) the introduction of the notion of fully specified queries that are semantically equivalent to a loosely-specified query; (2) a translation algorithm of a loosely-specified query into a set of semantically equivalent feasible query plans that are consistent with the binding patterns of query templates of the individual sources (capability descriptions in DIIM) and with interrelationships between information sources (expressed as join constraints in DIIM); and (3) a search restriction algorithm for optimizing query processing by pruning the search space into the relevant subspace of a query. The plans obtained by the proposed query planning process which is composed of the search restriction and translation algorithms can be shown to correspond to query plans semantically equivalent to the initial loosely-specified input query.