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Decision Trees
Decision trees are a method for defining complex relationships by
describing decisions and avoiding the problems in communication. A decision
tree is a diagram that shows alternative actions and conditions within
horizontal tree framework. Thus, it depicts which conditions to consider first,
second, and so on.
Decision trees depict the relationship of each condition and their
permissible actions. A square node indicates an action and a circle indicates a
condition. It forces analysts to consider the sequence of decisions and
identifies the actual decision that must be made.
The major limitation of a decision tree is that it lacks
information in its format to describe what other combinations of conditions you
can take for testing. It is a single representation of the relationships
between conditions and actions.
For example, refer the following decision tree −
Decision Tables
Decision tables are a method of describing the complex logical
relationship in a precise manner which is easily understandable.
· It is useful in
situations where the resulting actions depend on the occurrence of one or
several combinations of independent conditions.
· It is a matrix
containing row or columns for defining a problem and the actions.
Components
of a Decision Table
· Condition Stub − It is
in the upper left quadrant which lists all the condition to be checked.
· Action Stub − It is
in the lower left quadrant which outlines all the action to be carried out to
meet such condition.
· Condition Entry − It is
in upper right quadrant which provides answers to questions asked in condition
stub quadrant.
· Action Entry − It is
in lower right quadrant which indicates the appropriate action resulting from
the answers to the conditions in the condition entry quadrant.
The entries in decision table are given by Decision Rules which
define the relationships between combinations of conditions and courses of
action. In rules section,
- Y shows the existence
of a condition.
- N represents the
condition, which is not satisfied.
- A blank - against
action states it is to be ignored.
- X (or a check mark
will do) against action states it is to be carried out.
For example, refer the following table −
CONDITIONS |
Rule 1 |
Rule 2 |
Rule 3 |
Rule 4 |
Advance payment made |
Y |
N |
N |
N |
Purchase amount = Rs
10,000/- |
- |
Y |
Y |
N |
Regular Customer |
- |
Y |
N |
- |
ACTIONS |
||||
Give 5% discount |
X |
X |
- |
- |
Give no discount |
- |
- |
X |
X |
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