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What's new in DataFlex 2.2
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Dataflex multi-user features
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Workgroup kingpin
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A Circus Semantics for Ravenscar Protected Objects
The Ravenscar profile is a subset of the Ada 95 tasking model: it is certifiable, deterministic, supports schedulability analysis, and meets tight memory constraints and performance requirements. A central feature of Ravenscar is the use of protected objects to ensure mutually exclusive access to shared data. We give a semantics to protected objects using Circus, a combination of Z and CSP, and prove several important properties; this is the first time that these properties have been verified. Interestingly, all the proofs are conducted in Z, even the ones concerning reactive behaviour.
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The Value of Verification: Positive Experience of Industrial Proof
This paper describes the use of formal development methods on an industrial safety-critical application. The Z notation was used for documenting the system specification and part of the design, and the SPARK subset of Ada was used for coding. However, perhaps the most distinctive nature of the project lies in the amount of proof which was carried out: proofs were carried out both at the Z level -- approximately 150 proofs in 500 pages--and at the SPARK code level--approximately 9000 verification conditions generated and discharged. The project was carried out under UK Interim Defence Standards 00-55 and 00-56, which require the use of formal methods on safety-critical applications. It is believed to be the first to be completed against the rigorous demands of the 1991 version of these standards. 
 
The paper includes a comparison of proof with the various types of testing employed, in terms of their efficiency at finding faults. The most striking result is that the Z proof was substantially more efficient at finding faults than the most efficient testing phase. Given the importance of early fault detection, this helps to demonstrate the significant benefit and practicality of large-scale proof on projects of this kind.
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Towards an Integrated Model Checker for Railway Signalling Data
Geographic Data for Solid State Interlocking (SSI) systems detail site-specific behaviour of the railway interlocking. This report demonstrates how five vital safety properties of such data can be verified automatically using model checking. A prototype of a model checker for Geographic Data has been implemented by replacing the parser and compiler of NuSMV. The resulting tool, gdlSMV, directly reads Geographic Data and builds a corresponding representation on which model checking is performed using NuSMV's symbolic model checking algorithms.Because of the large number of elements in a typical track layout controlled by an SSI system, a number of optimisations had to be implemented in order to be able to verify the corresponding data sets.We outline how most of the model checking can be hidden from the user, providing a simple interface that directly refers to the data being verified.
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Type-Constrained Generics for Z
We propose an extension to Z whereby generic parameters may have their types partially constrained. Using this mechanism it becomes possible to define in Z much of its own schema calculus and refinement rules.
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‘The Standard Logic for Z’: A Clarification
Abstract. Some clarification is made of a recent article in Formal Aspects of Computing [Hen98]. Specifically, it is noted that the inconsistency found is in a draft logic, which is clearly unfinished. The latest news of the position of the Z Standards Panel on a logic for Z is given.