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Wrapping databases allows them to be reused in earlier unforeseen contexts, such as Web-based applications or federated systems. Data wrappers, and more specifically updating wrappers (that not only access legacy data but also update them), can provide external clients of an existing (legacy) database with a neutral interface and augmented capabilities. For instance, a collection of COBOL files can be wrapped in order to allow external application programs to access them through a relational, object-oriented or XML interface, while providing referential integrity control. We explore the principles of a wrapper architecture that addresses the problems of legacy data consistency management. The transformational paradigm is used as a rigorous formalism to define schema mappings as well as to generate as much as possible of the code of the wrappers. The generation is supported by an operational CASE tool.