Learn software concepts - Cleanroom Software Engineering - Certification

The verification and testing techniques leads to software components that can be certified. Certification implies that the reliability can be specified for each component. The potential impact of certifiable software components goes far beyond a single cleanroom project. Reusable software components can be stored along with their usage scenarios, program stimuli, and probability distributions.

The certification approach involves five steps :
1. Usage scenarios must be created.
2. A usage profile is specified.
3. Test cases are generated from the profile.
4. Tests are executed and failure data are recorded and analyzed.
5. Reliability is computed and certified.

Cleanroom Certification Models :
- Sampling model : Software testing executes m random test cases and is certified if no failures or a specified numbers of failures occur. The value of m is derived mathematically to ensure that required reliability is achieved.
- Component model : A system composed of n components is to be certified. The component model enables the analyst to determine the probability that component i will fail prior to completion.
- Certification model : The overall reliability of the system is projected and certified.

Learn software concepts - Cleanroom Software Engineering Cont...

The Cleanroom Software Engineering process is a software development process intended to produce software with a certifiable level of reliability. 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 semiconductors.

Central principles of Cleanroom Software Engineering :
- 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.

Advantages of Cleanroom Approach :
- Proven Practice : Several major products have been developed using Cleanroom and delivered to customers.
- Low Error Rate, highly reliable code.
- Increased Productivity.
- Can Be Incorporated Within A Quality Management Program Such As CMM Or ISO 9000.

Why are Cleanroom Techniques Not Widely Used ?
- Some people believe cleanroom techniques are too theoretical, too mathematical, and too radical for use in real software development.
- Relies on correctness verification and statistical quality control rather than unit testing (a major departure from traditional software development).
- Organizations operating at the ad hoc level of the Capability Maturity Model, do not make rigorous use of the defined processes needed in all phases of the software life cycle.

Learn software concepts - Cleanroom software engineering

Cleanroom software engineering is a formal approach to software development that can lead to software that has remarkably high quality. It uses box structure specification (or formal methods) for analysis and design modeling and emphasizes correctness verification, rather than testing, as the primary mechanism for finding and removing errors. Statistical use testing is applied to develop the failure rate information necessary to certify the reliability of delivered software.

The cleanroom approach begins with analysis and design models that use a box structure representation. A "box" encapsulates the system at a specific level of abstraction. Black boxes are used to represent the externally observable behavior of a system. State boxes encapsulate state data and operations. A clear box is used to model the procedural design that is implied by the data and operations of a state box.

Correctness verification is applied once the box structure design is complete. The procedural design for a software component is partitioned into a series of sub-functions. To prove the correctness of the sub-functions, exit conditions are defined for each sub-function and a set of sub-proofs is applied. If each exit is condition is satisfied, the design must be correct.

Once correctness verification is complete, statistical use testing commences. Unlike conventional testing, cleanroom software engineering does not emphasize unit or integration testing. Rather, the software is tested by defining a set of usage scenarios, determining the probability of use for each scenario, and then defining random tests that conform to the probabilities. The error records that result are combined with sampling, component, and certification models to enable mathematical computation of projected reliability for the software component.

The cleanroom philosophy is a rigorous approach to software engineering. It is a software process model that emphasizes mathematical verification of correctness and certification of software reliability. The bottom line is extremely low failure rates that would be difficult or impossible to achieve using less formal methods.