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A solution to the problem of supporting relational database operations despite domain mismatch is presented. Mismatched domains occur when information must be obtained from databases that were developed independently. Domain differences are resolved by mapping conflicting attributes to common domains by means of a mechanism of virtual attributes and then applying a set of extended relational operations to the resulting values. When one-one mappings cannot be established between domains, the values that result from attribute mappings may be partial. A set of extended relational operators that formalize operations over partial values and thus manipulate the incomplete information that results from resolving domain mismatch is defined.>
Linda G. DeMichiel (Sun,) studied this question.