4.5. Key Length Check

In step 1 of the CSDP we try to express information examples in terms of elementary facts. At that stage we rely on familiarity with the UoD to determine whether a fact type is simple or compound (splittable). Once uniqueness constraints are added, a formal check can be conducted in this regard. This section discusses a check based on uniqueness constraints, and the next section discusses the notions of projection and join, which may sometimes be used to perform a projection–join check.

Until we are experienced at conceptual schema design, we might include some fact types that are too long or too short. “Too long” means that the arity of the fact type is higher than it should be—the predicate has too many roles. In this ...

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