The paper is a tutorial review of program generators applied to simulation model building. A program generator is a tool to aid in the production of computer-coded representations of a logical model. A simple model introduces one generator, DRAFT. The application of the tool to a large engineering project is then used to highlight practical advantages and problems. The implications of the underlying network structure are considered. The presentation of development work illustrates the extent to which such modeling software can be extended. These extensions will support the model users in all aspects of decison making.