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The RDB DAS provides a straightforward mechanism for support of OptimisticConcurrencyControl. To enable OCC a client must designate an integer version column in the configuration (usually via a config xml file). The following example is an example of a cofig file that identifies a version column:

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When applying changes made to a graph (see ChangeSummaryProcessing), the DAS will throw an exception if any table row has been modified since the row was read. For example, if a DAS client reads a row representing a specific Customer and then tries to update that Customer, the DAS will throw an exception if the Customer has already been modified by some other agent. The following example illustrates applying changes and checking for a collision failure:

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