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Relational Integrity

I'm sure the topic of this section sounds suspiciously like some form of couples therapy. Not to fear—it's a good deal less interesting than that, unless you're a database designer, in which case it's endlessly fascinating.

Relational integrity, also known as referential integrity, speaks to the notion that a database structure, as expressed in an ERD, also implies certain rules about what can and cannot happen in a database. If you read Chapter 5, you encountered the concept of optionality rules. An optionality rule may, for example, assert that an order must have at least one order line item. Or it may assert the more obvious truth that an order line item that doesn't relate to an existing order is an error.


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