Information Modeling and Relational Databases, 2nd Edition

5.5. Logical Derivation Check

Step 3 of the design procedure included a check for basic arithmetic derivations— these are usually obvious (e.g., totals). Once uniqueness and mandatory role constraints are specified, we are in a good position to check for logical derivations — these can be harder to spot, especially if some important facts were missed at step 1.

As a simple example, consider the report extract shown in Table 5.14. You may recallthis table from the previous chapter, where it was correctly modeled as two binaries. We’ll now deliberately model it incorrectly to illustrate the logical derivation check. Suppose we verbalize the first row as the two facts: Lecturer ‘Halpin’ works for Department ‘CS’; Lecturer ‘Halpin’ works in Building ...