To manage this, a number of system development life cycle (SDLC) models have been created: waterfall, fountain, spiral, build and fix, rapid prototyping, incremental, and synchronize and stabilize.The oldest of these, and the best known, is the waterfall: a sequence of stages in which the output of each stage becomes the input for the next. These stages can be characterized and divided up in different ways, including the following: Project planning, feasibility study: Establishes a high-level view of the intended project and determines its goals. Systems analysis, requirements definition: Refines project goals into defined functions and operation of the intended application. Analyzes end-user information needs. Systems design: Describes desired features and operations in detail, including screen layouts, business rules, process diagrams, pseudocode and other documentation. Implementation: The real code is written here. Integration and testing: Brings all the pieces together into a special testing environment, then checks for errors, bugs and interoperability. Acceptance, installation, deployment: The final stage of initial development, where the software is put into production and runs actual business. Maintenance: What happens during the rest of the software's life: changes, correction, additions, moves to a different computing platform and more. This, the least glamorous and perhaps most important step of all, goes on seemingly forever.