It would be nice if a computer system could accept a program specification in the form of a mixed initiative dialogue. One capability such a system must have is the ability to ask questions in a coherent order. We will see a number of reasons it is better if such a system produces all the questions it can and has a "dialogue moderator" choose which to ask next, than if the system asks the first question it thinks of. DM, the dialogue moderator of PSI, chooses questions by searching a network model of a program, under control of a set of heuristic rules. This technique is simple and flexible.