Setting an attribute to unknown in a decision table

  The order in which logic is inferred is set in Blueriq and explained in Order and hierarchy in knowledge elements. In many cases, a business engineer will create a default value for an attribute - being the most frequent value - Decision tables and/or other logic elements infer the value of that attribute and if no inference is applicable, the default value is chosen. In short: default value is mainstream, the decision tables contain all exceptions.

No what if the exception is UNKNOWN?

So in most cases we know the value of an attribute, for instance 37, and in some specific cases it is unknown. In these situations, an action alternative will set the attribute to unknown, using the symbol * to achieve this.
(one might argue that the symbol ? would have been a better candidate for that)