Both Bayesian theory and Dempster-Shafer (evidence) theory assign non-negative weights to set of events. In Bayesian theory, the finite set of possible events denoted by , each individual event, is assigned a non-negative weight called probability denoted by . The probabilities satisfy the following properties.
In Dempster-Shafer theory, the finite set called frame of discernment, comprises all possible combination of events. Therefore, any subset of the frame of discernment can be assigned a non-negative weight called mass denoted by . The masses satisfy the following properties.
where is the empty set.
For example, a coin of two sides has two possible outcomes (events): head and tail. A Bayesian approach assigns probability individually to head and tail as and . DS theory would assign mass to each of the possibilities , , and . This allows DS theory to explicitly represent an ignorance or ambiguity (uncertainty) about the situation being observed. Refer ,  for more information about comparison of Bayesian theory and Dempster-Shafer theory.