Density Scores for Cooperative Query Answering.
Felix Naumann, Ulf Leser · 1999
Mediator-based information systems answer global queries by rewriting them into a combination of queries against physical data sources. One inherent assumption in most systems is that only a combination that satisfies the global query completely is considered valid, i.e., it must obtain values for each required attribute. Furthermore, most systems strive for complete answers, i.e., they try to access all relevant sources. These requirements frequently lead to a system behavior that entails a high potential for user frustration: In many scenarios a partially incomplete answer is much more appreciated than no answer at all. Also, obtaining the data from all sources, which can be very costly, is often not necessary. Based on this observation, we developed a cooperative query planning method. For a given query, the set of data sources is selected based on density scores obeying a userdefined price-constraint. The selection process naturally prefers complete answers, but can als...