ABSTRACT
Decision tables have been used to represent and analyze complex logical relationships since the early 1960s. They are ideal for describing situations in which a number of combinations of actions are taken under varying sets of conditions. Some of the basic decision table terms are illustrated in Table 7.1
A decision table has four portions: the part to the left of the bold vertical line is the stub portion; to the right is the entry portion. The part above the bold line is the condition portion, and below is the action portion. Thus, we can refer to
Table 7.1
Portions of a Decision Table
the condition stub, the condition entries, the action stub, and the action entries. A column in the entry portion is a rule. Rules indicate which actions are taken for the conditional circumstances indicated in the condition portion of the rule. In the decision table in 7.1, when conditions c1, c2, and c3 are all true, actions a1 and a2 occur. When c1 and c2 are both true and c3 is false, then actions a1 and a3 occur. The entry for c3 in the rule where c1 is true and c2 is false is called a “don’t care” entry. The don’t care entry has two major interpretations: the condition is irrelevant, or the condition does not apply. Sometimes people will enter the “n/a” symbol for this latter interpretation.
