91 research outputs found
Formal Verification of Real-Time Function Blocks Using PVS
A critical step towards certifying safety-critical systems is to check their
conformance to hard real-time requirements. A promising way to achieve this is
by building the systems from pre-verified components and verifying their
correctness in a compositional manner. We previously reported a formal approach
to verifying function blocks (FBs) using tabular expressions and the PVS proof
assistant. By applying our approach to the IEC 61131-3 standard of Programmable
Logic Controllers (PLCs), we constructed a repository of precise specification
and reusable (proven) theorems of feasibility and correctness for FBs. However,
we previously did not apply our approach to verify FBs against timing
requirements, since IEC 61131-3 does not define composite FBs built from
timers. In this paper, based on our experience in the nuclear domain, we
conduct two realistic case studies, consisting of the software requirements and
the proposed FB implementations for two subsystems of an industrial control
system. The implementations are built from IEC 61131-3 FBs, including the
on-delay timer. We find issues during the verification process and suggest
solutions.Comment: In Proceedings ESSS 2015, arXiv:1506.0325
Positioning Verfification in the Context of Software/System Certification
Formal verification applied to software has been seen as an important focus in research for determining the acceptability of that software for use. However, in examining the requirements for determining the safety of a software intensive system for use in critical situations, it is quite clear that verification plays a role,but not necessarily a central role. It is entirely possible that a piece of software satisfies its specification, but is unsafe to use. (The first and foremost reason for this is that the program satisfies an unsafe specification.) In this paper we will address the nature of certification in the context of critical systems, decomposing it,by means of a new philosophical framework, into four aspects: evidence, confidence, determination and certification. Our point of view is that establishing the safety (in a very general sense) of a system is a confidence building exercise much in the same vein as the scientific method; our framework serves as a setting in which we can properly understand and develop such an exercise. We will then place formal verification and assurance cases in this setting, discussing their roles and limitations.Keywords: Software certification, System certification, Formal specification, Verification,Critical systems, Safety, Assurance cases, Safety case
The C/C Genotype of the C957T Polymorphism of the Dopamine D2 Receptor is Associated with Schizophrenia
The T allele of the human dopamine D2 receptor (DRD2) gene C957T polymorphism is associated with reduced mRNA translation and stability. This results in decreased dopamine induced DRD2 upregulation and decreased in-vivo D2 dopamine binding. Conversely, the C allele of the C957T polymorphism is not associated with such changes in mRNA leading to increased DRD2 expression. PET and post-mortem binding studies show that schizophrenia is often associated with increased DRD2 availability. We report that on the basis of comparing the frequencies of the C/C and T/T genotypes of 153 patients with schizophrenia and 148 controls that schizophrenia is associated with the C/C genotype. The C957T shows a population attributable risk for schizophrenia of 24% and an attributable risk in those with schizophrenia of 42%. Increased expression of D2 receptors associated with the C allele is likely to be important in the underlying pathophysiology of at least some forms of schizophrenia. Enhanced understanding of schizophrenia afforded by this finding may lead to advances in treatment and prevention
Test Case Generation for Drivability Requirements of an Automotive Cruise Controller: An Experience with an Industrial Simulator
Automotive software development requires engineers to test their systems to
detect violations of both functional and drivability requirements. Functional
requirements define the functionality of the automotive software. Drivability
requirements refer to the driver's perception of the interactions with the
vehicle; for example, they typically require limiting the acceleration and jerk
perceived by the driver within given thresholds. While functional requirements
are extensively considered by the research literature, drivability requirements
garner less attention. This industrial paper describes our experience assessing
the usefulness of an automated search-based software testing (SBST) framework
in generating failure-revealing test cases for functional and drivability
requirements. Our experience concerns the VI-CarRealTime simulator, an
industrial virtual modeling and simulation environment widely used in the
automotive domain. We designed a Cruise Control system in Simulink for a
four-wheel vehicle, in an iterative fashion, by producing 21 model versions. We
used the SBST framework for each version of the model to search for
failure-revealing test cases revealing requirement violations. Our results show
that the SBST framework successfully identified a failure-revealing test case
for 66.7% of our model versions, requiring, on average, 245.9s and 3.8
iterations. We present lessons learned, reflect on the generality of our
results, and discuss how our results improve the state of practice.Comment: 10 pages papaer plus 2 of bibliography. 10 figures and 6 table
Novel Fundus Image Preprocessing for Retcam Images to Improve Deep Learning Classification of Retinopathy of Prematurity
Retinopathy of Prematurity (ROP) is a potentially blinding eye disorder
because of damage to the eye's retina which can affect babies born prematurely.
Screening of ROP is essential for early detection and treatment. This is a
laborious and manual process which requires trained physician performing
dilated ophthalmological examination which can be subjective resulting in lower
diagnosis success for clinically significant disease. Automated diagnostic
methods can assist ophthalmologists increase diagnosis accuracy using deep
learning. Several research groups have highlighted various approaches. This
paper proposes the use of new novel fundus preprocessing methods using
pretrained transfer learning frameworks to create hybrid models to give higher
diagnosis accuracy. The evaluations show that these novel methods in comparison
to traditional imaging processing contribute to higher accuracy in classifying
Plus disease, Stages of ROP and Zones. We achieve accuracy of 97.65% for Plus
disease, 89.44% for Stage, 90.24% for Zones with limited training dataset.Comment: 10 pages, 4 figures, 7 tables. arXiv admin note: text overlap with
arXiv:1904.08796 by other author
Is current incremental safety assurance sound ?
International audienceIncremental design is an essential part of engineering. Without it, engineering would not likely be an economic, nor an effective, aid to economic progress. Further, engineering relies on this view of incrementality to retain the reliability attributes of the engineering method. When considering the assurance of safety for such artifacts, it is not surprising that the same economic and reliability arguments are deployed to justify an incremental approach to safety assurance. In a sense, it is possible to argue that, with engineering artifacts becoming more and more complex, it would be economically disastrous to not “do” safety incrementally. Indeed, many enterprises use such an incremental approach, reusing safety artifacts when assuring incremental design changes. In this work, we make some observations about the inadequacy of this trend and suggest that safety practices must be rethought if incremental safety approaches are ever going to be fit for purpose. We present some examples to justify our position and comment on what a more adequate approach to incremental safety assurance may look like
Formalizing the Cardiac Pacemaker Resynchronization Therapy
For many years, formal methods have been used to design and develop critical systems in order to guarantee safety and security and the correctness of desired behaviours, through formal verification and validation techniques and tools. The development of high confidence medical devices such as the cardiac pacemaker, is one of the grand challenges in the area of verified software that need formal reasoning and proof-based development. This paper presents an example of how we used previous experience in developing a cardiac pacemaker using Event-B, to build an incremental proof-based development of a new pacemaker that uses Cardiac Resynchronization Therapy (CRT), also known as biventricular pacing or multisite pacing. In this work, we formalized the required behaviours of CRT including timing constraints and safety properties. We formalized the system using Event-B, and made use of the included Rodin tools to check the internal consistency with respect to safety properties, invariants and events. The system behaviours of the proven model were validated through the use of the ProB model checker
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