We show that production rules and persistent queues together provide a convenient mechanism for maintaining consistency in semantically heterogeneous multi-database environments. We describe a specification language and methods for automatically deriving production rules that maintain (1) existence dependencies, in which the presence of data in one database implies the presence of related data in another, and (2) value dependencies, in which the value of data in one database is based on the value of related data in another. The production rules derived from dependency specifications use persistent queues to monitor and maintain the dependencies automatically, asynchronously, incrementally, and correctly.
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