The authors present a technique for merging the schemas of heterogeneous databases that generalizes to several different data models, and show how it can be used in an interactive program that merges entity-relationship diagrams. Given a collection of schemas to be merged, the user asserts the correspondence between entities and relationships in the various schemas by defining 'isa' relations between them. These assertions are then considered to be elementary schemas, and are combined with the elementary schemas in the merge. Since the method defines the merge to be the join in an information ordering on schemas, it is a commutative and associative operation, which means that the merge is defined independent of the order in which schemas are presented. They briefly describe a prototype interactive schema merging tool that has been built on these principles.
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