The Data Model Scorecard™ contains over 400 rules to apply when reviewing a data model. One of these rules requires justifying optionality on a relationship. For example, on this model
We have these two business rules:
- Each Customer can place many Orders.
- Each Order must be placed by one Customer.
The circle on the relationship line implies zero. That is, a Customer can exist without ever placing an Order. In this example, we would ask the modeler the question, “When can a Customer exist without having placed an Order?”
Someone during a recent training class on the Scorecard asked why it is important to justify optionality such as in this example. Why do you think it is important?