4.3. Uniqueness Constraints on Longer Fact Types
This section shows how to specify uniqueness constraints on fact types of arity 3 and beyond, including nested versions. Let’s begin with an example. Figure 4.22 shows a populated ternary fact type of the form: Person scored Rating for Subject. For simplicity, assume that persons are identified just by their surname. Even if we are not familiar with the example, sample populations supplied by the domain expert can reveal that certain constraints don’t apply.
Figure 4.22. What are the uniqueness constraints?
Looking at the fact table, first consider each column individually. Each column has at ...
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