Importance

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Abstract

Techniques to extract, or unload, data from a database table based on a specific version of the table are described. Modern database management systems permit a user to change a databases' table structure or schema in response to changing operating conditions without blocking users' access to the underlying table or its data. Once modified, these database management systems permit data retrieval only in terms of a table's most recent version. Applications written to process a table's data in a first version may not be able to process data when that data is conformed to a later version. By providing a means to extract data from a table based on prior versions of that table, the invention permits users to evolve their database structure as needs require, while maintaining the ability to unload data for historical applications.

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First Claim