A probabilistic approach to query processing in heterogeneous database systems

In heterogeneous database systems, partial values can be used to resolve the interoperability problems, including domain mismatch, inconsistent data, and missing data. Performing operations on partial values may produce maybe tuples in the query result which cannot be compared. Thus, users have no way to distinguish which maybe tuple is the most possible answer. The concept of partial values is generalized to probabilistic partial values. The authors develop a full set of extended relational operators for manipulating relations containing probabilistic partial values. With this approach, the uncertain answer tuples of a query are associated with degrees of uncertainty. That provides users a comparison among maybe tuples and a better understanding on the query results. Besides, extended selection and join are generalized to α-selection and α-join, respectively, which can be used to filter out may be tuples with low possibilities-those which have possibilities smaller than α