Decision Table

A decision table represents the comlex decision logic associated with a data-processing job. A decision table summarized the action to be taken depending on the values of conditions that exist at the time the decision table is consulted. Decision tables override system flow charts in more complex circumstances, particularly those where several criteria determine an action, demand more specialized models.

A typical decision table is divided into 4 parts. They are –

1. Condition stub – which shows the conditions that determin which actions will result

2. Condition entries are the combination of conditions expressed as rules

3. Action stub which contains the possible actions which can occur as a result of the different condition combinations

4. Actions entries contains the action to be taken.

The simplest type of decision table is a limited entry decision table in which conditions are expressed as questions that may be answered as questions that may be answered as questions that may be answered by a Y/N. The condition entries are then specified as combinations of these answers. The relevant action fo each combination of conditions is recorded by an ‘x’ in the action stub. A general form of a decision table is show below –

If n states in one condition and m states in the second condition. The number of columns is given by m xn (extended entry decision table). In general, if there are n conditions having only 2 states, then the number of columns is given as 2ⁿ (limited entry decision table). Therefore for a decision table having 4 statements each having two states (Y/N) can have 2⁴ = 16 columns.