Formal Aspects of Computing最新文献

Class invariants — consistency constraints preserved by every operation on objects of a given type — are fundamental to building, understanding and verifying object-oriented programs. For verification, however, they raise difficulties, which have not yet received a generally accepted solution. The present work introduces a proof rule meant to address these issues and allow verification tools to benefit from invariants.

It clarifies the notion of invariant and identifies the three associated problems: callbacks, furtive access and reference leak. As an example, the 2016 Ethereum DAO bug, in which $50 million were stolen, resulted from a callback invalidating an invariant.

The discussion starts with a simplified model of computation and an associated proof rule, demonstrating its soundness. It then removes one by one the three simplifying assumptions, each removal raising one of the three issues, and leading to a corresponding adaptation to the proof rule. The final version of the rule can tackle tricky examples, including “challenge problems” listed in the literature.

Our study aims to illustrate the clinical picture of otosclerosis in patients and the effect of surgery on the bone conduction thresholds compared to audiometry tests before surgery. A retrospective study included 36 patients that fit the inclusion criteria based on the patient's files and Pure Tone Audiometry of the patients before and after surgery. The questionnaire used is attached at the end of the study. According to Our sample, 77.8% were females, and 22.2% were males. The youngest was 17 years old, the eldest was 61, and the mean age was 38.2 years old. Hearing loss was the most common symptom in 100% of patients, while tinnitus was found in 66.7% and vertigo in 11%. The Injury was bilateral in 72% of the cases. Before surgery, the mean air conduction threshold (ACT) was 54.7 dB, the mean value of the air-bone gap (ABG) was 38.3 dB, and the mean bone conduction threshold (BCT) was 16.1 dB. Meanwhile, after the surgery, the mean BCT was 18.2 dB. Otosclerosis is more common in middle-aged females. Most cases are bilateral. Two-thirds of the cases of hearing loss were associated with tinnitus, while only a few had vertigo. A slight increase was noticed in BCTs after surgeries, especially at 4000 Hz. Stapedectomy caused a noticeable decrease in the values of BCTs on the frequency 4000 Hz. Stapedotomy improved the BCTs after surgery by about 5.3 dB at 4000 Hz.

The reliability and safety of complex software systems are provided by extracting safety requirements from regulations and operational environments and later specifying these requirements precisely. At the early stage, these extracted safety requirements are informal. Typically, they cope with non-functional requirements. Analysis of early requirements using traditional methods is inadequate because these methods only focus on the WHAT dimension of requirements engineering but do not address the WHY dimension of requirements engineering. In this article, we are using a goal-oriented modelling method called iStar to confront these issues. To ensure that the software system developed fulfils the requirements specified in the early-phase, it is necessary to integrate early-phase requirements with late-phase requirements. To accomplish this task, in this article, we use Z formal method to integrate early-phase requirements with late-phase requirements. This integration synergistically resolves the above issues. As a case study, we use the CBTC moving block interlocking system to illustrate the synergy of the iStar and Z combination on complex software systems. Finally, we verify the developed formal model against LTL safety properties using the ProZ model checking tool.

The behavior and architecture of large scale discrete state systems found in computer software and hardware can be specified and analyzed using a particular class of primitive recursive functions. This paper begins with an illustration of the utility of the method via a number of small examples and then via longer specification and verification of the ”Paxos” distributed consensus algorithm[26]. The “sequence maps” are then shown to provide an alternative representation of deterministic state machines and algebraic products of state machines.

Distributed and composite systems, parallel and concurrent computation, and real-time behavior can all be specified naturally with these methods - which require neither extensions to the classical state machine model nor any axiomatic methods or other techniques from formal logic or other foundational methods. Compared to state diagrams or tables or the standard set-tuple-transition-maps, sequence maps are more concise and better suited to describing the behavior and compositional architecture of computer systems. Staying strictly within the boundaries of classical deterministic state machines anchors the methods to the algebraic structures of automata and makes the specifications faithful to engineering practice.