Browsing by Author "Duan, Lian"

Now showing 1 - 5 of 5
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    Cyber-Physical System Requirements - A Model Driven Approach
    (2013) Murugesan, Anitha; Duan, Lian; Rayadurgam, Sanjai; Heimdahl, Mats
    Systems where the physical world interacts extensively with often distributed and networked-software are referred to as Cyber-Physical Systems (CPS). Gathering and analyzing CPS requirements poses unique challenges to the requirements engineering community - a perspective that is sensitive to the scoping and interplay between the cyber, physical and behavioral aspects of the system. The major challenges were identifying and analyzing (1)requirements to address the complexity in the continuous domain, (2)requirements related to the continual behavior of the system, (3)the precise scope of the system, (4)requirements flow down during system decomposition, (5)mode logic and features interactions and, (6)system behavior during mode transitions. Unfortunately there is little guidance in the literature to systematically address these issues. We pursued a model-driven approach to overcome these challenges, which we believe is broadly applicable to CPS requirements elicitation and specification. The variety of modeling techniques we used, served as a crucial aid in the elicitation and discovery of requirements and provided an initial classification of the types of requirements and modeling patterns needed to describe crucial aspects of a CPS. We used a generic patient controlled analgesia (GPCA) infusion pump system as case example to investigate the requirements of a medical CPS and provide an archetype of system development artifacts that could serve as a generic reference standard used by CPS researchers and practitioners.
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    From Requirements to Code: Model Based Development of A Medical Cyber Physical System?
    (2014) Murugesan, Anitha; Heimdahl, Mats; Whalen, Michael; Rayadurgam, Sanjai; Komp, John; Duan, Lian; Kim, Baek-Gyu; Sokolsky, Oleg; Lee, Insup
    The advanced use of technology in medical devices has improved the way health care is delivered to patients. Unfortunately, the increased complexity of modern medical devices poses challenges for development, assurance, and regulatory approval. In an eort to improve the safety of advanced medical devices, organizations such as FDA have supported exploration of techniques to aid in the development and regulatory approval of such systems. In an ongoing research project, our aim is to provide effective development techniques and exemplars of system development artifacts that demonstrate state of the art development techniques. In this paper we present an end-to-end model-based approach to medical device software development along with the artifacts created in the process. While outlining the approach, we also describe our experiences, challenges, and lessons learned in the process of formulating and analyzing the requirements, modeling the system, formally verifying the models, generating code, and executing the generated code in the hardware for generic patient controlled analgesic infusion pump (GPCA). We believe that the development artifacts and techniques presented in this paper could serve as a generic reference to be used by researchers, practitioners, and authorities while developing and evaluating cyber physical medical devices.
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    Modeling and Requirements on the Physical Side of Cyber-Physical Systems
    (IEEE, 2013) Heimdahl, Mats; Duan, Lian; Murugesan, Anitha; Rayadurgam, Sanjai
    In a cyber-physical system (a system where the physical world interacts extensively with—often networked— software), the physical portion of the system resides in the continuous and continual domain. Thus, on the physical side of cyber-physical systems we will have to contend with not only real time requirements but also the continuous and continual nature of the system. This poses a new set of challenges for requirements engineering; we must write well defined requirements to address crucial issues not commonly addressed in the software domain. For example, the rate of change of a controlled variable, the time it takes for a controlled variable to settle sufficiently close to a set-point, and the cumulative errors built up over time may be of critical importance. In this paper we outline how early modeling in the continuous domain serves as a crucial aid in the elicitation and discovery of requirements for cyber-physical systems and provide an initial classification of the types of requirements needed to describe crucial aspects of the physical side of a cyber-physical system.
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    Reasoning about Confidence and Uncertainty in Assurance Cases: A Survey
    (2014) Duan, Lian; Rayadurgam, Sanjai; Heimdahl, Mats; Ayoub, Anaheed; Sokolsky, Oleg; Lee, Insup
    Assurance cases are structured logical arguments supported by evidence that explain how systems, possibly software systems, satisfy desirable properties for safety, security or reliability. The confidence in both the logical reasoning and the underlying evidence is a factor that must be considered carefully when evaluating an assurance case; the developers must have confidence in their case before the system is delivered and the assurance case reviewer, such as a regulatory body, must have adequate confidence in the case before approving the system for use. A necessary aspect of gaining confidence in the assurance case is dealing with uncertainty, which may have several sources. Uncertainty, often impossible to eliminate, nevertheless undermines confidence and must therefore be sufficiently bounded. It can be broadly classified into two types, aleatory (statistical) and epistemic (systematic). This paper surveys how researchers have reasoned about uncertainty in assurance cases. We analyze existing literature to identify the type of uncertainty addressed and distinguish between qualitative and quantitative approaches for dealing with uncertainty.
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    Representation of Confidence in Assurance Case Evidence
    (2015) Duan, Lian; Rayadurgam, Sanjai; Heimdahl, Mats; Sokolsky, Oleg; Lee, Insup
    When evaluating assurance cases, being able to capture the confidence one has in the individual evidence nodes is crucial, as these values form the foundation for determining the confidence one has in the assurance case as a whole. Human opinions are subjective, oftentimes with uncertainty---it is difficult to capture an opinion with a single probability value. Thus, we believe that a distribution best captures a human opinion such as confidence. Previous work used a doubly-truncated normal distribution or a Dempster-Shafer theory-based belief mass to represent confidence in the evidence nodes, but we argue that a beta distribution is more appropriate. The beta distribution models a variety of shapes and we believe it provides an intuitive way to represent confidence. Furthermore, there exists a duality between the beta distribution and subjective logic, which can be exploited to simplify mathematical calculations. This paper is the first to apply this duality to assurance cases.