Dealing with Uncertainty in Situation Assessment: towards a Symbolic
  Approach
  The situation assessment problem is considered, in terms of object,
condition, activity, and plan recognition, based on data coming from the
real-word {em via} various sensors. It is shown that uncertainty issues are
linked both to the models and to the matching algorithm. Three different types
of uncertainties are identified, and within each one, the numerical and the
symbolic cases are distinguished. The emphasis is then put on purely symbolic
uncertainties: it is shown that they can be dealt with within a purely symbolic
framework resulting from a transposition of classical numerical estimation
tools.
