Eliciting Background Information for Safety-Critical Software Specifications

Authors:Knight, JC, Department of Computer ScienceUniversity of Virginia Nakano, LG, Department of Computer ScienceUniversity of Virginia Sarkov, A, Department of Computer ScienceUniversity of Virginia

Experience has shown that many defects in software systems are introduced during the specification phase. For safety - critical systems this is significant since it indicates where progress might be made in improving dependability. In this paper we argue that one of the reasons that defects are introduced during specification is that the specifier does not have an adequate understanding of the background and context of the system being specified. In order to provide a better basis for specification, we introduce the notion of prespect'flcati0n--the determination and documentation of as much of the relevant background and context information as possible for the benefit of the specifier. The specifier is often a software engineer. Though qualified to build software, he or she is unlikely to have a detailed knowledge of the application domain. Quite inadvertently, software engineers are likely to overlook aspects of the system that may have direct or indirect safety consequences. Application experts, on the other hand, are typically not trained to build software and therefore to understand its safety implications. To develop correct specifications, it is essential that there be precise communication between the domain expert and the software engineer. In this paper, we propose the introduction of a phase in the software lifecycle for safety - critical systems that should precede the requirements analysis and documentation phases. We call this phase the prespeczfication
phase. In this phase, pertinent background information regarding the software to be developed is collected and documented without undertaking a full requirements elicitation. The document that is generated is called the prespecificatian
document. We have built a prespecification
document for a realistic safety - critical application. This application is a digital control system for the University of Virginia's Research Nuclear Reactor and a software specification for the digital control system is now being developed using the prespecification. We use the this prespecification
as an example throughout this paper.
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Source Citation:

Knight, JC, LG Nakano, and A Sarkov. "Eliciting Background Information for Safety-Critical Software Specifications." University of Virginia Dept. of Computer Science Tech Report (1995).

University of Virginia, Department of Computer Science
Published Date: