Web services for higher integrity instrument control

This paper relates the experience in using a modified life cycle development process which is proposed herein for integrity planning applied to web services as reusable software components in order to enhance the web services' reliability, safety, and security in an instrument control environment. Using the integrity-enhanced lifecycle, a test bed instrument control system is developed using .NET web services. A commercial web service is also included in the test bed system for comparison. Both systems are monitored over a one-year period and failure data is collected. For a further comparison, a similar instrument control system is developed to a high quality pedigree but lacking the focus on integrity and reusable components. Most of the instrumentation is the same between the two systems; however, the comparative system uses a more traditional approach with a single, integrated software control package. As with the test bed system, this comparative system is monitored over a one-year period. The data for the two systems is compared and the results demonstrate a significant increase in integrity for the web service-based test bed system. The failure rate for the test bed system is approximately 1 in 8100 as compared to 1 in 1600 for the comparison system.