1. An expert system shell comprising: (a) a computer having a display device, an entry device, and a memory for string a knowledge base; said knowledge base comprising: (1) variables having values represented by tables of probabitlity distributions keyed by zero, one or more formal parameters; (2) functions defining relationships between the values of each dependent variable and the values of its corresponding argument variables; (3) means for computing the probability distribution of the values of a dependent variable from the probability distribution of the values of the corresponding argument variables; and (b) means for propagating the consequences of a change in the value of a variable to maintain the functional relationships among a selected subset of the dependent variables.
1. An expert system shell comprising: (a) a computer having a display device, an entry device, and a memory for string a knowledge base; said knowledge base comprising: (1) variables having values represented by tables of probabitlity distributions keyed by zero, one or more formal parameters; (2) functions defining relationships between the values of each dependent variable and the values of its corresponding argument variables; (3) means for computing the probability distribution of the values of a dependent variable from the probability distribution of the values of the corresponding argument variables; and (b) means for propagating the consequences of a change in the value of a variable to maintain the functional relationships among a selected subset of the dependent variables. 9. The system of claim 1, said propagating means further comprising means for minimizing the computation required during propagation by assuring that the final distributions for all arguments to a function are known before the distribution for the dependent variable is computed.