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Chapter 9 • proCess speCifiCations and struCtured deCisions 247

Figure 9.13
Rules
Conditions and Actions 12 3 4 5 6 7 Checking the decision table for
inadvertent contradictions and
Condition 1 Y Y Y Y Y N N redundancy is important.
Condition 2 Y Y Y N N Y N
Condition 3 N N Y
Action 1 X X X
Action 2 X X
Action 3 X X

Contradiction Redundancy

side, with the root of the tree on the left side of the paper; from there, the tree branches out to
the right. This orientation allows the analyst to write on the branches to describe conditions and
actions.
Unlike the decision tree used in management science, the analyst’s tree does not contain
probabilities and outcomes. In systems analysis, trees are used mainly for identifying and orga-
nizing conditions and actions in a completely structured decision process.

Drawing Decision Trees
It is useful to distinguish between conditions and actions when drawing decision trees. This
distinction is especially relevant when conditions and actions take place over a period of time
and their sequence is important. For this purpose, use a square node to indicate an action and a
circle to represent a condition. Using notation makes the decision tree more readable, as does
numbering the circles and squares sequentially. Think of a circle as signifying IF, whereas the
square means THEN.
When decision tables were discussed in an earlier section, a point-of-sale example was
used to determine the purchase approval actions for a department store. Conditions included the
amount of the sale (under $50) and whether the customer paid by check or credit card. The four

COnsUlting OppORtUnity 9.4

A Tree for Free

“I know you’ve got a plane to catch, but let me try to explain it the mileage is doubled no matter what day, and if it is the 17th
to you once again, sir,” pleads Glen Curtiss, a marketing manager leg traveled, the mileage is tripled. If the traveler booked the
for Premium Airlines. Curtiss has been attempting (unsuccess- flight on the Web or through a travel service such as Orbitz or
fully) to explain the airline’s new policy for accumulating miles for Travelocity, 100 miles are added.
awards (such as upgrades to first class and free flights) to a member “I hope that clears it up for you, Mr. Icarus. Enjoy your
of Premium’s “Flying for Prizes” club. flight, and thanks for flying Premium.”
Glen takes another pass at getting the policy off the ground, Mr. Icarus, whose desire to board the Premium plane has
saying, “You see, sir, the traveler (that’s you, Mr. Icarus) will be all but melted away during Glen’s long explanation, fades into
awarded the miles actually flown. If the actual mileage for the leg the sea of people wading through the security lanes, without
was less than 500 miles, the traveler will get 500 miles credit. If the so much as a peep in reply.
trip was made on a Saturday, the actual mileage will be multiplied Develop a decision tree for Premium Airlines’ new pol-
by two. If the trip was made on a Tuesday, the multiplication factor icy for accumulating award miles so that the policy becomes
is 1.5. If this is the ninth leg traveled during the calendar month, clearer, is easier to grasp visually, and hence is easier to explain.