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Designing a Data Warehouse: Supporting Customer Relationship Management by Chris Todman

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CONSTRAINTS

Part of the role of the logical model is to record constraints that need to be imposed on the model. The introduction of full support for time brings with it some additional requirements for the imposition of constraints.

Double-Counting Constraints

Double-counting occurs when the joining of tables returns more rows than should be returned. This problem is usually avoided if the general rules about the structure of dimensional models are followed.

However, the introduction of existence attributes into the model increases the risk of error by changing the nature of the relationships in the warehouse data model from simple (1:n) to complex (m:n).

The problem is best described by the use of an example of a sale of wine. Table 6.2 shows ...

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