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UML and Data Modeling: A Reconciliation by David Hay

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There are more flexible ways to categorize things, of course, but these should be represented in a data model separately, without using sub-types. Figure 4-6 shows a reasonable way to do this for Party, by adding the entity classes Party Category and Party Categorization. A Party Categorization is the fact that a particular Party falls into a particular Party Category for a period of time. That is, each Party Categorization must be of exactly one Party into exactly one Party Category—at a particular time. The Party Categorization is effective on an Effective Date, and ceases to be effective on an Until Date.

This structure allows a Party to be categorized into multiple Party Categories at a time, and also allows for that Party ...

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