session is over, the prototyper constructs a throwaway prototype on top of the baseline system. The user now uses the new system and evaluates. If the new changes aren't effective, the prototyper removes them. If the user likes the changes, the prototyper writes feature-enhancement requests and forwards them to the development team. The development team, with the change requests in hand from all the sites, then produce a new evolutionary prototype using conventional methods. Obviously, a key to this method is to have well trained prototypers available to go to the user sites. The operational prototyping methodology has many benefits in systems that are complex and have few known requirements in advance. Evolutionary systems development Evolutionary Systems Development is a class of methodologies that attempt to formally implement evolutionary prototyping. One particular type, called Systemscraft is described by John Crinnion in his book Evolutionary Systems Development. Systemscraft was designed as a 'prototype' methodology that should be modified and adapted to fit the specific environment in which it was implemented. Systemscraft was not designed as a rigid 'cookbook' approach to the development process. It is now generally recognised[sic] that a good methodology should be flexible enough to be adjustable to suit all kinds of environment and situation... The basis of Systemscraft, not unlike evolutionary prototyping, is to create a working system from the initial requirements and build upon it in a series of revisions. Systemscraft places heavy emphasis on traditional analysis being used throughout the development of the system. Evolutionary rapid development Evolutionary Rapid Development (ERD) was developed by the Software Productivity Consortium, a technology development and integration agent for the Information Technology Office of the Defense Advanced Research Projects Agency (DARPA). Fundamental to ERD is the concept of composing software systems based on the reuse of components, the use of software templates and on an architectural template. Continuous evolution of system capabilities in rapid response to changing user needs and technology is highlighted by the evolvable architecture, representing a class of solutions. The process focuses on the use of small artisan-based teams integrating software and systems engineering disciplines working multiple, often parallel short-duration timeboxes with frequent customer interaction. Key to the success of the ERD-based projects is parallel exploratory analysis and development of features, infrastructures, and components with and adoption of leading edge technologies enabling the quick reaction to changes in technologies, the marketplace, or customer requirements. To elicit customer/user