The challenge of designing better interactive systems has not gone unnoticed in software engineering. Boehm observes that the dominant waterfall model of development "does not work well for many classes of software, particularly interactive end-user applications."[4 ] His proposal, a "spiral model" of software development, incorporates user involvement, prototyping, and iterative design. Yourdon recently wrote, "the first, and by far the most important, player in the systems game is someone known to systems analysts as a user.