Today there was a post at the LinkedIn group “Looking for a simple example of representing calculations in a Decision Model” with this problem description:

“Trying to determine the risk of meeting a Werewolf based upon two factors: Phase of the Moon, and Distance from Graveyard. But I can’t seem to put these together into a complete Decision Model:

Fact Type: Phase of the Moon
Values: New Moon, Half Moon, Three-Quarter Moon, Full Moon
Rule Family: Phase of the Moon Risk
Conditions Conclusions
New Moon .01
Half Moon .25
Three-Quarter Moon .50
Full Moon .75

Fact Type: Miles from Graveyard
Values: < 5 miles, between {5 miles, 25 miles}, > 25 miles
Rule Family: Miles from Graveyard Risk
Conditions Conclusions
<5 miles .75
between {5 miles, 25 miles} .25
> 25 miles .01

Fact Type: Werewolf Risk
Values: Phase of the Moon, Miles from Graveyard
Rule Family: Werewolf Risk Weights
Conditions Conclusion
Phase of the Moon .75
Miles from Graveyeard .5

Calculate Werewolf Risk:
(Phase of the Moon weight * Phase of the Moon Risk) + (Miles from Graveyard Risk * Miles from Graveyard Risk) = Werewolf Risk”

Instead of figuring out if this is a joke or not, I could not resist a temptation to quickly implement the proper decision model. “Would I be able to do within 1 hour?” – was my question. I did. Here is the Excel-based decision “DetermineRiskOfMeetingWerewolf”

and supporting decision tables:

The calculation rules for the total risk to meet a werewolf may look as follows:

The Glossary for this problem:

I also needed to create a few test cases. Here they are (again in Excel table that define a new type “Werewolf” and two cases “John” and “Mary”:

When I ran this model I received the following output:

You may look at the complete decision model by opening this Excel file. The entire OpenRules project can be downloaded from http://openrules.com/downloads/my/DecisionWerewolf.zip. If you add this project to an OpenRules workspace, you may execute this model against your own test cases.