Six-sigma software using cleanroom software engineering techniques - Motorola's hardware-quality approach applied to software - includes related article on legal primitive evaluation - Technical

Hewlett-Packard Journal, June, 1994 by Grant E. Head

There is also evidence that the resulting product is significantly more concise and compact than the industry average.(6) This further enhances productivity. Not only is the product produced at a high statement-per-month rate, but the total number of statements is also smaller.

Needed Best Practices

Cleanroom is compatible with most industry-accepted best practices for software generation. It is not necessary to unlearn anything. Some of these best practices are required (such as a structured design methodology). Others such as software reuse are optional but compatible.

As mentioned above, cleanroom requires some sort of structured design methodology. It has been successfully employed using a number of different design approaches. Most recently however, the cleanroom originators are recommending a form of object-oriented design.(7)

All cleanroom deliverables must be subject to inspections, code walkthroughs, or some other form of rigorous peer review. It is not critical what form is applied. What is critical is that 100% of all deliverables be subjected to this peer-review process and that it be done in small quantities. For instance, it is recommended that no more than three to five pages of a code module be inspected at a single inspection.

Required New Features

In addition to the standard software engineering practices mentioned above, there are a number of cleanroom-specific processes that are required or are recommended. These practices include structured specifications, functional verification, structured data, and statistical testing. Structured specifications are applied to the project before design begins. This strongly affects the delivery schedule and the project management process. Functional verification is applied during design, coding, and inspection processes. Structured data is applied during the design process. Finally, statistical testing is the integration testing methodology of choice. Fig. 2 summarizes the cleanroom processes.

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Structured Specifications

Structured specifications(8) is a term applied to the process used to divide a product specification into small pieces for implementation. It is not critical exactly how this division is accomplished as long as the results have the following characteristics:

* Each specification segment must be small enough so that it can be fully implemented by the development team within days or weeks rather than months or years.

* The result of implementing each segment must be a module that can be completely executed and tested on its own. This means that no segment can contain partially implemented features that must be avoided during testing to prevent program failure.

* The segments may not have mutual dependencies. For example, it is satisfactory for segment 4 to require the implementation of segment 3 to execute correctly. It is assumed that segment 3 will be implemented first and will exist to support the testing of segment 4. However, it is not satisfactory for segment 3 to require segment 4 to execute properly at the same time.