Two different tasks can have two different levels of "integrity" desired. For example, the task of mailing a thank-you note to all customers might not care if o

Two different tasks can have two different levels of "integrity" desired. For example, the task of mailing a thank-you note to all customers might not care if one customer accidentally has two addresses or none. For the task of billing customers, we probably want an exact one-to-one customer to mailing address. If someone protects me with the constraint of one-to-one customer to address, then maybe I lose the fact that the customer has just opened a second office. All I'm saying is that database constraints go both ways, they reveal bugs and they cause bugs.