Performing operations over mismatched domains

A solution is proposed to the problem of providing support for operations over partially matched domains. Mismatched domains occur when information must be obtained from databases that were developed independently. Domain differences are resolved by mapping conflicting attributes to a common domain and the applying a set of extended relational operations to the resulting values. The values that result from attribute mappings can be total or partial. Some of the theoretical issues involved in this approach are discussed, and a set of extended relational operators that formalize operations across partial values is defined.<>