Cleanroom Software Engineering

For the meaning of Cleanroom engineering as a method to avoid copyright infringement, see Clean room design.

The Cleanroom Software Engineering process is a software development process intended to produce software with a certifiable level of reliability. The Cleanroom process was originally developed by Harlan Mills and several of his colleagues at IBM^[1]. The focus of the Cleanroom process is on defect prevention, rather than defect removal. The name Cleanroom was chosen to evoke the cleanrooms used in the electronics industry to prevent the introduction of defects during the fabrication of integrated circuits. The Cleanroom process first saw use in the mid to late 80s. Demonstration projects within the military began in the early 1990s^[2]. Recent work on the Cleanroom process has examined fusing Cleanroom with the automated verification capabilities provided by specifications expressed in CSP^[3].

Central principles

The basic principles of the Cleanroom process are

Software development based on formal methods

Cleanroom development makes use of the Box Structure Method to specify and design a software product. Verification that the design correctly implements the specification is performed through team review.

Incremental implementation under statistical quality control

Cleanroom development uses an iterative approach, in which the product is developed in increments that gradually increase the implemented functionality. The quality of each increment is measured against pre-established standards to verify that the development process is proceeding acceptably. A failure to meet quality standards results in the cessation of testing for the current increment, and a return to the design phase.

Statistically sound testing

Software testing in the Cleanroom process is carried out as a statistical experiment. Based on the formal specification, a representative subset of software input/output trajectories is selected and tested. This sample is then statistically analyzed to produce an estimate of the reliability of the software, and a level of confidence in that estimate.