This paper is concerned with the problem of measuring the uncertainty in a
broad class of belief networks, as encountered in evidential reasoning appl
ications. In our discussion, we give an explicit account of the networks co
ncerned, and coin them the Dempster-Shafer (D-S) belief networks. We examin
e the essence and the requirement of such an uncertainty measure based on w
ell-defined discrete event dynamical systems concepts. Furthermore, we exte
nd the notion of entropy for the D-S belief networks in order to obtain an
improved optimal dynamical observer. The significance and generality of the
proposed dynamical observer of measuring uncertainty for the D-S belief ne
tworks lie in that it can serve as a performance estimator as well as a fee
dback for improving both the efficiency and the quality of the D-S belief n
etwork-based evidential inferencing. We demonstrate, with Monte Carte simul
ation, the implementation and the effectiveness of the proposed dynamical o
bserver in solving the problem of evidential inferencing with optimal evide
nce node selection.