 Exclusionary syntax
The following examples are also logically equivalent:
Figure 75. Exclusionary Logic Using Boolean Condition, Pt. 1 Figure 76. Exclusionary Logic Using Boolean Condition, Pt. 2 Figure 77. Exclusionary Logic Using Negated Value Notice that that the last example uses the unary function not, described in more detail in the Rule Language Guide, to negate the value 747 selected from the Values set.
Once again we see that the same rule can be expressed in different ways on the Rulesheet, with identical results. It is left to the rule modeler to decide which way of expressing the rule is preferable in a given situation. We recommend, however, avoiding double negatives. Most people find it easier to understand attribute=T instead of attribute<>F, even though logically the two expressions are equivalent
Note: This assumes bi-value logic. If tri-value logic is assumed (such as, for a non-mandatory attribute), meaning the null value is available in addition to true and false, then these two expressions are not equivalent. If attribute = null, then the truth value of attribute<>F is true while that of attribute=T is false.