decision table&tree

7/31/2019 Decision Table&Tree

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Decision Tables

A Decision table is a table of rows and columns, separated

into four quadrants and is designed to illustrate complex

decision rules

Condition Stub upper left quadrant

Rules Stub upper right quadrant

Action Stub bottom left quadrant

Entries Stub - bottom right quadrant

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Decision Table Layout Standard format used for presenting decision tables.

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DecisionStub

RulesStub

ActionStub

EntriesStub


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Decision Table Example

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1 2 3 4

Like Boss? Y Y N N

20% Pay Raise? Y N Y N

Stay Another Year X X

Quit after 2 Months X

Quit next Week X


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Developing Decision Tables Process requires the determination of the number ofconditions (inputs) that affect the decision.

The set of possible actions (outputs) must likewise be

determined

The number of rules is computed

Each rule must specify one or more actions

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Number of Rules

Each condition generally has two possible

alternatives (outcomes): Yes or No

In more advanced tables, multiple outcomes for eachcondition are permitted

The total number of rules is equal to

2 no. of conditions

Thus, if there are four conditions, therewill be

sixteen possible rulesDoneb

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Building the Table

For each rule, select the appropriate action and indicatewith an X

Identify rules that produce the same actions and attempt tocombine those rules; for example:

Condition 1 Y Y Condition 1 Y

Condition 2 Y N Condition 2 -

Action 1 X X Action 1 X

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Cleaning Things Up

Check the table for any impossible situations,

contradictions, and redundancies and eliminate such rules

Rewrite the decision table with the most reduced set of

rules; rearranging the rule order is permissible if it improvesuser understanding

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Decision Table example: combine

and reduce

Conditions and Actions 1 2 3 4 5 6 7 8

Order from Fall Catalog Y Y Y Y N N N N

Order from Christmas Catalog Y Y N N Y Y N N

Order from Special Catalog Y N Y N Y N Y NMail Christmas Catalog X X X X

Mail Special Catalog X X

Mail Both Catalogs X X

The four gray columns canbe combined into a singlerule. Note that four each,there was NO order placedfrom the Special Catalog.

In addition, Rules 1&5 andRules 3&7 can be combined.Each pair produces the same

action and each pair shares twocommon conditions.


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Decision Table example ~ Final

Version

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Conditions and Actions 1 2 3

Order from Fall Catalog -- -- --Order from Christmas Catalog Y -- N

Order from Special Catalog Y N Y

Mail Christmas Catalog X

Mail Special Catalog XMail Both Catalogs X

Eliminates the need to check for every possible case.


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Decision Table example:checking for completeness and accuracy

Doneby:mahmoudabudagga

Conditions and Actions 1 2 3 4

Salary > $50,000 per year Y Y N N

Salary < $2,000 per month Y N Y NAward Double Bonus X

Award Regular Bonus X

Award no Bonus X

Although the Y-N Combinations suggest a rule, in thiscase, it is impossible for conditions 1 & 2 to exist

simultaneously. They are in complete contradictionwith each other. In the final version of the table,

Rule 1 will disappear and Rules -4 will become Rules 1-3.


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Decision Tables and

Membership Tables


X X XX X

X X X

Action 1Action 2

Action 3

Y Y Y Y N N NN

Y Y N N Y Y NN

Y N Y N Y N YN

Condition 1

Condition 2

Condition 3

Rules

1 2 3 4 5 6 7 8

Conditions and

Actions

NNNN

NYYN

NYNY

YYYY

ABABBA

OperationsSets


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Importance of Decision Tables

Aids in the analysis of structured decisions

Ensures completeness

Checks for possible errors (impossible situations,

contradictions, and redundancies, etc.) Reduces the amount of condition testing that must be done



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Decision Trees

Decision trees are useful when multiple branching occurs in a

structured decision process, although they can be quite

effective when only two decision paths are called for.

They are helpful when necessary to maintain a certain order

for a series of decisions.



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Drawing Decision Trees

Drawn horizontally

Root of tree is to the

left side

Square Nodesindicate actions

Circle Nodes

represent possible

conditions

Circle is analogous to

the condition part of

an IF statement

Square is analogousto the consequent of

an IF statement (the

THEN part)

IF Circle THEN

SquareDoneby:mahmoudabudagga


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Decision Tree Example


1

2

3

4Ring up sale

5Look up card in book

6

Call supervisor for approval

7 Call bank for approval

denotes end

of action

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