Page 281 -

248 part 3 • the analysis proCess

Figure 9.14 Complete the sale after verifying signature.
Check 3
Drawing a decision tree to show
the noncash purchase approval 2 Credit Card
actions for a department store. Under $50 Complete the sale. No signature needed.
4
1
≥ $50 Call supervisor for approval.
Check 6

5 Credit Card Communicate electronically with bank for
credit card authorization.
7

actions possible were to: complete the sale after verifying the signature; complete the sale with
no signature needed; call the supervisor for approval; or communicate electronically with the
bank for credit card authorization. Figure 9.14 illustrates how this example can be drawn as a
decision tree. In drawing the tree:
1. Identify all conditions and actions and their order and timing (if they are critical).
2. Begin building the tree from left to right, making sure you list all possible alternatives
before moving to the right.

This simple tree is symmetrical, and the four actions at the end are unique. A tree does not need
to be symmetrical. Most decision trees have conditions that have a different number of branches.
Also, identical actions may appear more than once.
A decision tree has three main advantages over a decision table. First, it takes advantage
of the sequential structure of decision tree branches so that the order of checking conditions
and executing actions is immediately noticeable. Second, conditions and actions of decision
trees are found on some branches but not on others; in contrast, with decision tables, conditions
and actions are all part of the same table. Conditions and actions that are critical are connected
directly to other conditions and actions, whereas conditions that do not matter are absent. In
other words, the tree does not have to be symmetrical. Third, compared with decision tables,
decision trees are more readily understood by others in an organization. Consequently, they are
more appropriate as a communication tool.

Choosing a Structured Decision Analysis Technique
We have examined the three techniques for analysis of structured decisions: structured English,
decision tables, and decision trees. Although they need not be used exclusively, it is customary
to choose one analysis technique for a decision rather than employing all three. The following
guidelines provide you with a way to choose one of the three techniques for a particular case:
1. Use structured English when
a. There are many repetitious actions,
OR
b. Communication to end users is important.
2. Use decision tables when
a. Complex combinations of conditions, actions, and rules are found,
OR
b. You require a method that effectively avoids impossible situations, redundancies, and
contradictions.
3. Use decision trees when
a. The sequence of conditions and actions is critical,
OR
b. When not every condition is relevant to every action (the branches are different).