Decision Tables
A useful testing technique and
more…
Marien de Wilde, Solution Architect
In this session …
 Definition
 Application areas
 Steps to create a
decision table
 Exercise
 Solution to exercise
February 2010
2
Definition
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
Combinations
Values 1 2 3 4 5 6 7 8
Y, N
Y Y Y Y NNNN
Y, N
Y Y NNY Y NN
Y, N
Y NY NY NY N
X
X
X
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X
X
X
 Components
 A decision table lists
causes and effects in a
matrix. Each column
represents a unique
combination.
 Purpose is to structure
logic
Cause = condition
Effect = action = expected results
3
Application Areas
 Business Analysis
 Programming
 Testing
 Hardware Design
 etc
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4
Steps to Create a decision table
1. List all causes in the decision table
2. Calculate the number of possible
combinations
3. Fill columns with all possible
combinations
4. Reduce test combinations
5. Check covered combinations
6. Add effects to the table
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Step 1: List all causes
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
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Values
Y, N
Y, N
Y, N
Hints:
Combinations
1 2 3 4 5 6
7 8Write down the values
Y Y Y Y NNNN
Y Y N N Y Y N Nthe cause/condition
Y NY NY NY N
can assume
X
X
XCluster related causes
X
X
X
 Put the most
dominating cause first
 Put multi valued
causes last
6
Step 2: Calculate combinations
Number of Values to  If all causes are simply Y/N
the power of the
values:
number of causes
2number of causes
with these values
 If 1 cause with 3 values and 3
with 2:
31 * 23 = 24
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 Or, use the Values column
and multiply each value
down the column, eg.
3*2*2*2=24
7
es
e1
e2
e3
ts
t1
t2
Step 3: Fill columns
Combinations
Values 1 2 3 4 5 6 7 8
Y, N
Y Y Y Y NNNN
Y, N
Y Y NNY Y NN
Y, N
Y NY NY NY N
X
X
X
X
X
X
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 Algorithm:
1. Determine Repeating Factor (RF):
divide remaining combinations by the
number of possible values for that
cause
2. Write RF times the first value, then
RF times the next etc. until row is full
3. Next row, go to 1.
8
Step 4: Reduce combinations
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
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Combinations
Values 1 2 3 4 5 6 7 8
Y, N
Y Y Y Y NNNN
Y, N
Y Y NNY Y NN
Y, N
Y N - - Y NY N
X
X
X
X
X
X
Combinations
Values 1 2 3 4 5 6 7
Y, N
Y Y Y NNNN
Y, N
Y Y NY Y NN
Y, N
Y N - Y NY N
X
X
X
 Find indifferent
combinations – place
a ‘-’
X
X
 Join columns where
columns are identical
 Tip: ensure the effects
are the same
9
Step 5: Check covered
combinations
 Checksum
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
Checksum
Combinations
Values 1 2 3 4
Y, N
Y Y Y N
Y, N
Y N N Y, N
- Y N -
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X
2
 For each column calculate the
X
1
1
4
8
combinations it represents
 A ‘-’ represents as many
combinations as the cause has
 Multiply for each ‘-’ down the
column
 Add up total and compare with
step 2
10
Step 6: Add effects to table
Causes
Cause 1
Cause 2
Cause 3
Effects
Effect 1
Effect 2
Checksum
Combinations
Values 1 2 3 4
Y, N
Y Y Y N
Y, N
Y N N Y, N
- Y N -
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X
X
2
X
X
1
1
4
 Read column by
column and determine
the effects
 One effect can occur
in multiple test
8 combinations
11
Exercise: Specification
Create a decision table
A mailing is to be sent out to customers. The
content of the mailing is about the current level
of discounting and potential levels of
discounting. The content is different for different
types of customers.
Customer Types A, B and C get a normal letter
except Customer Type C, who get a special letter.
Any customer with 2 or more current lines or
with a credit rating of ‘X’ get a special paragraph
added with an offer to subscribe to another level
of discounting.
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Solution on next slide
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Exercise: possible solution
Causes
Customer Type
2 or more lines
Credit rating = X
Effects
Normal Letter
Special Letter
Add. Paragraph
No Letter
Checksum
Values
A,B,C,O
Y, N
Y, N
1
A
Y
Y
2
A
Y
N
3
A
N
Y
4
A
N
N
5
B
Y
Y
6
B
Y
N
Combinations
7 8 9 10 11 12
B B C C C C
N N Y Y N N
Y N Y N Y N
X X X X X X X X
? X X
? X X
X X X X
? X X
1 1 1 1 1 1 1 1 1 1
1
1
13
O
Y
Y
14
O
Y
N
15
O
N
Y
16
O
N
N
?
?
?
?
1
?
?
?
?
1
?
?
?
?
1
?
?
?
?
1
16
“2 or more current lines OR credit rating X”. What if both: AND?
Other customer types? See “O-Other” above.
What about non current lines?
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Thank You
February 2010
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