Thus, the Heart Failure Program consists of a set of knowledge bases and a number of operators that take input about a patient from the user, build a patient specific model, and provide mechanisms for the user to understand the analyses of the operators. This structure of many operators and multiple reasoning strategies, provides a flexibility that does not limit the ways in which the user can apply the program. The user is able to concentrate on questions of diagnosis, if that is what is important in the case, or move on to the potential effects of therapies if that is what is important. In real cases, it is clear that these issues are closely interrelated and the program allows the user to move back and forth between diagnosis and management considerations as appropriate. The other advantage of this structure is the power gained by each operator by building on the conclusions of previous operators. For example, the diagnostic process is simplified because definite conclusions have already been made and these can be handled as if they were additional input constraining the possible conclusions.