Exposing inconsistencies can uncover many defects in software specifications. One approach to exposing inconsistencies analyzes two redundant specifications, one operational and the other property-based, and reports discrepancies. This paper describes a "practical" formal method, based on this approach and the SCR (software cost reduction) tabular notation, that can expose inconsistencies in software requirements specifications. Because users of the method do not need advanced mathematical training or theorem-proving skills, most software developers should be able to apply the method without extraordinary effort. This paper also describes an application of the method which exposed a safety violation in the contractor-produced software requirements specification of a sizable, safety-critical control system. Because the enormous state space of specifications of practical software usually renders direct analysis impractical, a common approach is to apply abstraction to the specification. To reduce the state space of the control system specification, two "pushbutton" abstraction methods were applied, one which automatically removes irrelevant variables and a second which replaces the large, possibly infinite, type sets of certain variables with smaller type sets. Analyzing the reduced specification with the model checker Spin uncovered a possible safety violation. Simulation demonstrated that the safety violation was not spurious but an actual defect in the original specification.

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This article describes a formal analysis technique, called consistency checking , for automatic detection of errors, such as type errors, nondeterminism, missing cases, and circular definitions, in requirements specifications. The technique is designed to analyze requirements specifications expressed in the SCR (Software Cost Reduction) tabular notation. As background, the SCR approach to specifying requirements is reviewed. To provide a formal semantics for the SCR notation and a foundation for consistency checking, a formal requirements model is introduced; the model represents a software system as a finite-state automation which produces externally visible outputs in response to changes in monitored environmental quantities. Results of two experiments are presented which evaluated the utility and scalability of our technique for consistency checking in real-world avionics application. The role of consistency checking during the requirements phase of software development is discussed.

The paper describes a class of formal analysis called consistency checking that mechanically checks requirements specifications, expressed in the SCR tabular notation, for application independent properties. Properties include domain coverage, type correctness, and determinism. As background, the SCR notation for specifying requirements is reviewed. A formal requirements model describing the meaning of the SCR notation is summarized, and consistency checks derived from the formal model are described. The results of experiments to evaluate the utility of automated consistency checking are presented. Where consistency checking of requirements fits in the software development process is discussed.

This paper introduces MT, a collection of integrated tools for specifying and analyzing real-time systems using the Modechart language. The toolset includes facilities for creating and editing Modechart specifications. Users may symbolically execute the specifications with an automatic simulation tool to make sure that the specified behavior is what was intended. They may also invoke a verifier that uses model-checking to determine whether the specifications imply (satisfy) any of a broad class of safety assertions. To illustrate the toolset's capabilities as well as several issues that arise when formal methods are applied to real-world systems, the paper includes specifications and analysis procedures for a software component taken from an actual Naval real-time system.>