The inference engine activates all the production rules in order to produce the solution degrees DS(x,y).

In a first approach, we have chosen to use each rule as an additional confirmation (resp. invalidation) and to consider each knowledge unit as strengthening (resp. weakening) the problem solution . Each rule is applied independently on each point and produces a new degree of solution computed from the initial neutral value .

So for each point and for each rule we have the following process :

Note that uncertainly management appears at two levels in the deductive process.

If the rule is for example : IF solution THEN A ( )

• importance degree of the rule
• realization degree of conclusion A

Then we use a MYCIN [BS84] like algorithm.