## Inference Algorithms

#### Basic Goal for Inference

All rules have the basic format:
If condition
Then Conclusion
Want to interpret conditions with current data
• When current data make condition true, then know corresponding Conclusion
• Want to keep making inferences until know enough about desired results
• Can think of reasoning as giving a chain from original data to results

### Two Basic Approaches for Reasoning

#### Forward Chaining

Work left to right in diagram, from known data toward results
• Apply as many rules as you can
• Reach as many conclusions as possible
• Stop when a desired result found
OR
• Stop when you cannot infer any more

#### Backward Chaining

Work right to left in diagram, from possible results toward known data
• Look at desired result variable(s)
• Determine what rules might allow you to conclude result
• Identify hypotheses that would allow rule to apply
• If data known, determine if conditions for rule met
• If data not known, determine what rules allow data to be inferred

 created May 13, 2003 last revised May 13, 2003 previous   next