What is a Cleanroom approach?

In this article we discuss the cleanroom approach in detail. The size of the team is usually small and is divided in to following three sub – teams:

1. Specification team: This team is responsible for the development and maintenance of the specifications.
2. Development team: This team is responsible for the development and verification of the software.
3. Certification team: This team is responsible for the development of statistical tests and reliability growth models. 

The incremental development is always carried out under statistical quality control so that the performance can be assessed at the end of every iteration using the following measures:

1. Errors per KLOC
2. Rate of growth in MTTF
3. Number of sequential error free tests.

The software development in cleanroom approach is purely based up on the mathematical principles whereas the testing is based up on the statistical principles. 

- Firstly, the system to be developed is formally specified and an operational profile is created. This profile and the formal specifications are then used to define the software increments which are then used for the two purposes namely:

1. Construction of a structured program
2. Designing of statistical tests: These tests also contribute to the first purpose.

- The constructed program is then formally verified and integrated with the increment.

Below mentioned is the flow of cleanroom approach:

1. Software requirements specification
2. Software design and development
3. Incremental software delivery
4. Incremental statistical testing
5. Regression testing
6. Software reliability measurement
7. Process error diagnosis and correction

- The incremental development planning is divided in to two parts namely:

1. Functional specification: It involves formal design correctness verification.
2. Usage specification: It involves statistical test case generation.

- Both these processes then merge down to statistical testing which then follows quality certification model and MTTF estimates.

- The whole cleanroom project develops around the incremental strategy. 

- Requirements are gathered from the customers and elicited and refined via the traditional methods.

- The definition of the data, its behavior and procedures are isolated and separated by the box structures at every level of refinement. 

- Specifications or the black boxes when iteratively refined become state boxes i.e., architectural designs and clear boxes i.e., the component–level designs.

- Formal inspections are carried out to make sure that the code confirms to standards, it is syntactically correct and its correctness has been verified. 

- Statistical usage planning involves creation of tests cases that match with the probability distribution of the usage pattern

- In place of the exhaustive testing, a sample of all the test cases is employed. 

- Once the programmers are done with all 3 activities (i.e., verification, inspection, usage testing, and defect removal) the increment is considered to be certified and ready to be integrated. 

- For developing a right system, customer feedback and involvement are 2 necessary elements throughout the process. 

- Increment planning is required so that the customer’s system requirements can be clarified. 

- There is a requirement of management of resources and control of complexity which is also achieved through incremental planning.

- In order to develop a quality product a control over the software development cycle and process measurement is very much required.

- Following are the benefits of concurrent planning:

1. Concurrent engineering
2. Step wise integration
3. Continuous quality feedback
4. Continuous customer feedback
5. Risk management
6. Change management

- All of the above benefits are achieved respectively by:

1. Certification and scheduling parallel development
2. Testing cumulative increments
3. Statistical process control
4. Through actual use
5. Treatment of the high risk elements in early phases
6. Systematic accommodation of the changes

Design verification advantage allows the cleanroom teams to verify each and every line of code.