Decision Table

• A decision determines an output from a number of inputs by applying some logic.
• Decisions can be decomposed into two sub-decisions:

  • Top level
  • Lower level
• Top level decisions can be thought of as selecting an answer from a range of possible answers.
• Lower level decisions often will simply provide input to other decisions.
• Decision Trees represent decisions as a sequence of steps, while Decision Tables describes all possible combinations of conditions and the decision appropriate to each combination.
• Levels of uncertainty can also be built into decision trees to account for the relative probabilities of the various outcomes.
• Determine the correct types of decision graphs:

  A) Decision Tree

  B) Decision Table

  
• Decision trees are a graphical representation of rules, where:

  • An inner node corresponds to a decision
  • An edge represents an alternative value for the decision
  • A leaf node representing an effect
• Input the correct terms:

  A) Edge

  B) Inner Node

  C) Leaf Node

  
• Input the correct terms:

  A) Outcomes

  B) Conditions

  C) Actions

  D) Conditions tested

  E) Possible actions

  
• A decision table is a precise way of modelling logic as it helps organise the possible decision outcome combinations into a compact manner.
• When there is a large number of logical alternatives, it would be more convenient to use a flowchart instead of a decision table.
• There are three types of decision tables:

  • Limited Entry Decision Tables
  • Extended Entry Decision Tables
  • Mixed Entry Decision Tables
• When omitting a column in a decision table, use an * to indicate that not outcomes exist for that specified combination.
• In a decision table, redundancies have to be removed in order to simplify the table. This is done so by merging columns with the same outcomes.
• Advantages of Decision Tables:

  • Possible to check all combinations
  • Shows the cause and effect relationship
  • Easy to trace from actions to combinations
  • Compact and easier to follow a column
• Flaws of Decision Tables:

  • Large decision tables can be incomprehensible and difficult to modify
  • Flowcharts are better to express the total sequence of events needed to solve a problem
  • Flowcharts are more familiar