Bayesian network: It is essentially an expert system in which the uncertainty is dealt with using the conditional probabilities and Bayes' Theorem. Formally such type of network comprises the following:
* A set of directed edges between the variables and a set of variables.
* Each variable has the ?nite set of the states which are mutually exclusive.
* The variables together with directed edges forma the conditional independence of the graph.
* To each of the variable A with parents B1; ... ; Bn there is an attached conditional probability table Pr A B1; B2; ... ; Bn .
An instance is shown in the Figure drawn below in which cancer is independent of age group given exposure to the toxics and smoking.