A-level Computing/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Problem Solving/Decision tables

Structure charts Finite state machines 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: The four quadrants 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. Printer troubleshooter 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         Example: Decision Tables Let's take a look at a computer game example, for a football simulation the following rules are set up. Rules Conditions 90 minutes Y Y Y Team A Winning Y Team B Winning Y Y Draw Y Actions Game Over X X Team A Wins X Team B Wins X Extra Time X Keep Playing X X What happens when: 90 minutes up the game is a draw Answer: Keep Playing and give them some extra time Exercise: Decision Tables Create a decision table for the following program in an office email system Send email when Recipient address present, subject present, before 5:30pm If after 5:30pm then put in pending folder If Recipient address missing or subject message, give warning message This question is open to interpretation, but you should have something resembling this: Rules Conditions Address Present Y Y Y Subject Present Y Y Y Before 5:30 Y Y Y Actions Send Mail X Error Message X X Make pending X Describe the use of Decision Tables Determine logical conditions and consequential actions. Structure charts Finite state machines