THE INCREMENTAL DEVELOPMENT PROCESS IN CLEANROOM SOFTWARE ENGINEERING

The objective of this paper is to present the theoretical basis and pr actical application of incremental development in the Cleanroom softwa re engineering process. Incremental development is based on the mathem atical principle of referential transparency. Cleanroom uses increment al development to build systems in a succession of cumulative subsets of user function. The increments accumulate top-down into the final pr oduct in a development and certification pipeline. Increment planning occurs after top-level specification, and results in a construction pl an for the software. Factors determining the composition of increments include clarity of requirements, usage probability of user functions, reliability requirements for subsystems, coordination with the hardwa re development schedule, dependencies between functions, complexity, r euse, or other factors that pose risks to the project. Each increment involves a complete development and certification cycle. The first inc rement is a minimal system, and the final increment is the complete sy stem. User feedback on each increment is a gauge on whether the right system is being built, and quality measures in each increment are a ga uge on whether the system is being built right. Benefits of incrementa l development include customer feedback on the evolving system, intell ectual control of the technical work, and management control of the sc hedule and budget. While incremental development may be used with othe r development methods, it is particularly effective when used with the formal methods in the Cleanroom process.