A-level Computing/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Problem Solving/Decision tables
Decision tables are compact and precise ways of modelling complicated logic, such as that which you might use in a computer program. They do this by mapping the different states of a program to an action that a program should perform. Decision tables take on the following format:
| Conditions | Condition alternatives |
| Actions | Action entries |
The limited-entry decision table is the simplest to describe. The condition alternatives are simple Boolean values, and the action entries are check-marks, representing which of the actions in a given column are to be performed.
A technical support company writes a decision table to diagnose printer problems based upon symptoms described to them over the phone from their clients. They type the following data into the advice program:
- Printer does print
- Red light is flashing
- Printer is recognised
The program then uses the decision table to find the correct actions to perform, namely that of Check / Replace ink.
| Rules | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Conditions | Printer does not print | Y | Y | Y | Y | N | N | N | N |
| A red light is flashing | Y | Y | N | N | Y | Y | N | N | |
| Printer is unrecognised | Y | N | Y | N | Y | N | Y | N | |
| Actions | Check the power cable | X | |||||||
| Check the printer-computer cable | X | X | |||||||
| Ensure printer software is installed | X | X | X | X | |||||
| Check/replace ink | X | X | X | X | |||||
| Check for paper jam | X | X | |||||||
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Example: Decision Tables Let's take a look at a computer game example, for a football simulation the following rules are set up.
What happens when:
Answer: Keep Playing and give them some extra time | |||||||||||||||||||||||||||||||||||||||||||||||||||||
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Exercise: Decision Tables Create a decision table for the following program in an office email system
Answer: This question is open to interpretation, but you should have something resembling this:
Describe the use of Decision Tables Answer: Determine logical conditions and consequential actions. | ||||||||||||||||||||||||||||||||||||||