4.Decision Tables

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Decision Tables

March 13, 2014

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Possible solution to the last exercise

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Decision Tables and Decision Trees

Precise and compact way to model complicated logic

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Specifies a system as

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Specifies a system as a set of possible conditions,

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Specifies a system as a set of possible conditions, rules for reacting to stimuli when those conditions are met, and

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Specifies a system as a set of possible conditions, rules for reacting to stimuli when those conditions are met, and specific actions to be taken as a result.

Makes user requirements omissions and/or contradictionsexplicit so that the SE can go back to the client and ask specificquestions regarding whatto do whenthese conditions arise.

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Structure

Rows in the table are of two types: condition rows and actionrows.

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Structure


A column represents a combination of condition outcomes andthe corresponding actions to take.

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Structure



also referred to as a rule

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Structure



also referred to as a rule A complete decision table specifies one rule for each combination ofthe condition outcomes.

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Structure



also referred to as a rule A complete decision table specifies one rule for each combination ofthe condition outcomes. A decision table contains redundancy if there exists two columnsthat are equivalent.

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Structure




A complete decision table specifies one rule for each combination ofthe condition outcomes. A decision table contains redundancy if there exists two columnsthat are equivalent.

A decision table is ambiguous or contradictory if, for the samecombination of condition outcomes, the specified actions are different.

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Structure




A complete decision table specifies one rule for each combination ofthe condition outcomes. A decision table contains redundancy if there exists two columnsthat are equivalent.

A decision table is ambiguous or contradictory if, for the samecombination of condition outcomes, the specified actions are different. A decision table is correct if it has neither redundancies norcontradictions.

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Example

A technical support company writes a decision table to diagnose

printer problems based on the symptoms described to them over thephone by the client.

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Example

A technical support company writes a decision table to diagnose

printer problems based on the symptoms described to them over thephone by the client.

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Methodology1. Identify conditions and values.

Find the data attribute each condition tests and all of theattributes values.

2. Identify possible actions. Determine each action to be taken for each decision or policy.

3. Compute the maximum number of rules.

4. Enter all possible rules. Fill in the values of the condition data attributes in eachnumbered rule column

5. Define actions for each rule. For each rule, mark the appropriate actions with an X in thedecision table.

6. Verify the policy. Review completed decision table with end-users.

7. Simplify the table. Eliminate and/or consolidate rules to reduce the number ofcolumns.

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ExampleThe structure English or pseudocode specification of the processtake speeding decision is:

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ExampleThe structure English or pseudocode specification of the processtake speeding decision is:

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Decision Tree

A tree in which a non-leaf node includes a condition to evaluate.

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Decision Tree


The edges of a non-leaf node represent the outcomes of decisionsmade at that node.

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Decision Tree


The edges of a non-leaf node represent the outcomes of decisionsmade at that node.

A decision tree is a binary tree if all outcomes are binary,meaning that their outcome is either true or false.

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Documents

4.Decision Tables