Universität Stuttgart
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Item Open Access A Bayesian network approach to assess and predict software quality using activity-based quality models(2009) Wagner, StefanAssessing and predicting the complex concept of software quality is still challenging in practice as well as research. Activity-based quality models break down this complex concept into more concrete definitions, more precisely facts about the system, process and environment and their impact on activities performed on and with the system. However, these models lack an operationalisation that allows to use them in assessment and prediction of quality. Bayesian Networks (BN) have been shown to be a viable means for assessment and prediction incorporating variables with uncertainty. This paper describes how activity-based quality models can be used to derive BN models for quality assessment and prediction. The proposed approach is demonstrated in a proof of concept using publicly available data.Item Open Access Empirical research plan: effects of sketching on program comprehension(2016) Baltes, Sebastian; Wagner, StefanSketching is an important means of communication in software engineering practice. Yet, there is little research investigating the use of sketches. We want to contribute a better understanding of sketching, in particular its use during program comprehension. We propose a controlled experiment to investigate the effectiveness and efficiency of program comprehension with the support of sketches as well as what sketches are used in what way.Item Open Access A comprehensive safety engineering approach for software-intensive systems based on STPA(2015) Abdulkhaleq, Asim; Wagner, Stefan; Leveson, NancyFormal verification and testing are complementary approaches which are used in the development process to verify the functional correctness of software. However, the correctness of software cannot ensure the safe operation of safety-critical software systems. The software must be verified against its safety requirements which are identified by safety analysis, to ensure that potential hazardous causes cannot occur. The complexity of software makes defining appropriate software safety requirements with traditional safety analysis techniques difficult. STPA (Systems-Theoretic Processes Analysis) is a unique safety analysis approach that has been developed to identify system hazards, including the software-related hazards. This paper presents a comprehensive safety engineering approach based on STPA, including software testing and model checking approaches for the purpose of developing safe software. The proposed approach can be embedded within a defined software engineering process or applied to existing software systems, allow software and safety engineers integrate the analysis of software risks with their verification. The application of the proposed approach is illustrated with an automotive software controller.Item Open Access DNS of multiple bubble growth and droplet formation in superheated liquids(2018) Loureiro, Daniel Dias; Reutzsch, Jonathan; Dietzel, Dirk; Kronenburg, Andreas; Weigand, Bernhard; Vogiatzaki, KonstantinaFlash boiling can occur in rocket thrusters used for orbital manoeuvring of spacecraft as the cryogenic propellants are injected into the vacuum of space. For reliable ignition, a precise control of the atomization process is required as atomization and mixing of fuel and oxidizer are crucial for the subsequent combustion process. This work focuses on the microscopic process leading to the primary break-up of a liquid oxygen jet, caused by homogeneous nucleation and growth of vapour bubbles in superheated liquid. Although large levels of superheat can be achieved, sub-critical injection conditions ensure distinct gas and liquid phases with a large density ratio. Direct numerical simulations (DNS) are performed using the multiphase solver FS3D. The code solves the incompressible Navier-Stokes equations using the Volume of Fluid (VOF) method and PLIC reconstruction for the phase interface treatment. The interfaces are tracked as multiple bubbles grow, deform and coalesce, leading to the formation of a spray. The evaporation rate at the interface and approximate vapour properties are based on pre-computed solutions resolving the thermal boundary layer surrounding isolated bubbles, while liquid inertia and surface tension effects are expected to play a major role in the final spray characteristics which can only be captured by DNS. Simulations with regular arrays of bubbles demonstrate how the initial bubble spacing and thermodynamic conditions lead to distinct spray characteristics and droplet size distributions.Item Open Access Do code clones matter?(2009) Juergens, Elmar; Deißenböck, Florian; Hummel, Benjamin; Wagner, StefanCode cloning is not only assumed to inflate maintenance costs but also considered defect-prone as inconsistent changes to code duplicates can lead to unexpected behavior. Consequently, the identification of duplicated code, clone detection, has been a very active area of research in recent years. Up to now, however, no substantial investigation of the consequences of code cloning on program correctness has been carried out. To remedy this shortcoming, this paper presents the results of a large-scale case study that was undertaken to find out if inconsistent changes to cloned code can indicate faults. For the analyzed commercial and open source systems we not only found that inconsistent changes to clones are very frequent but also identified a significant number of faults induced by such changes. The clone detection tool used in the case study implements a novel algorithm for the detection of inconsistent clones. It is available as open source to enable other researchers to use it as basis for further investigations.Item Open Access Modelling the quality economics of defect-detection techniques(2006) Wagner, StefanThere are various ways to evaluate defect-detection techniques. However, for a comprehensive evaluation the only possibility is to reduce all influencing factors to costs. There are already some models and metrics for the cost of quality that can be used in that context. These models allow the structuring of the costs but do not show all influencing factors and their relationships. This paper proposes an analytical model for the economics of defect-detection techniques that can be used for analysis and optimisation of the usage of such techniques. In particular we analyse the sensitivity of the model and how the model can be applied in practice.Item Open Access Acoustic and seismic emissions from wind turbines(2017) Calarco, Francesca; Cheng, Po Wen; Zieger, Toni; Ritter, JoachimWith regards to the interdisciplinary “TremAc” Project funded by the German Federal Ministry for Economic Affairs and Energy, this paper examines acoustic and seismic emissions generated by wind turbines with the aim of identifying a better understanding of their interaction. Measurement campaigns will be carried out in the field around a single wind turbine plant and results in terms of acoustic and seismic signals will be correlated and then evaluated in relation to environmental factors such as wind speed, wind direction and temperature as well as to data related to the wind turbines-specifications (e.g. rotation speed).Item Open Access Synchronisierung von digitalen Modellen mit realen Fertigungszellen auf Basis einer Ankerpunktmethode am Beispiel der Automobilindustrie(2017) Ashtari Talkhestani, Behrang; Schlögl, Wolfgang; Weyrich, MichaelDie zunehmende Produktvielfalt und die Verkürzung der Produktlebenszyklen erfordern eine schnelle und kostengünstige Rekonfiguration bestehender Produktionssysteme [1]. Um diesen Herausforderungen zu begegnen, ist ein aktuelles digitales Modell der bestehenden Fertigungszelle, im Folgenden Digitaler Zwilling genannt, eine geeignete Lösung. Der Digitale Zwilling führt zu einer Kostenreduktion durch Verkürzung der Umrüstzeiten durch virtuelle Planung und Simulation basierend auf dem aktuellen Zustand der realen Produktionsanlage als auch durch eine frühzeitige Erkennung von Konstruktions- oder Prozessablauffehlern in der Produktionsanlage. Voraussetzung für die Verwendbarkeit des Digitalen Zwillings vom Produktionssystem ist allerdings, dass ein aktuelles (virtuelles) Anlagenmodell von den mechatronischen Bestandteilen der realen Anlage während der verschiedenen Phasen ihres Lebenszyklus existiert. In diesem Beitrag wird die domänenübergreifende, mechatronische Datenstruktur der virtuellen Fertigungszellen in der Automobilindustrie diskutiert. Es wird eine systematische Ankerpunktmethode vorgestellt, mithilfe derer die Abweichungen zwischen den virtuellen Modellen und der Realität detektiert und ermittelt werden können. Basierend darauf wird eine sogenannte regelbasierte Konsistenzprüfung zur durchgängigen, domänenübergreifenden Synchronisierung der aktuellen mechatronischen Ressourcenkomponenten der Produktionssysteme mit deren virtuellem Anlagemodell vorgestellt.Item Open Access Software quality models : purposes, usage scenarios and requirements(2009) Deißenböck, Florian; Juergens, Elmar; Lochmann, Klaus; Wagner, StefanSoftware quality models are a well-accepted means to support quality management of software systems. Over the last 30 years, a multitude of quality models have been proposed and applied with varying degrees of success. Despite successes and standardisation efforts, quality models are still being criticised, as their application in practice exhibits various problems. To some extent, this criticism is caused by an unclear definition of what quality models are and which purposes they serve. Beyond this, there is a lack of explicitly stated requirements for quality models with respect to their intended mode of application. To remedy this, this paper describes purposes and usage scenarios of quality models and, based on the literature and experiences from the authors, collects critique of existing models. From this, general requirements for quality models are derived. The requirements can be used to support the evaluation of existing quality models for a given context or to guide further quality model development.Item Open Access A model and sensitivity analysis of the quality economics of defect-detection techniques(2006) Wagner, StefanOne of the main cost factors in software development is the detection and removal of defects. However, the relationships and influencing factors of the costs and revenues of defect-detection techniques are still not well understood. This paper proposes an analytical, stochastic model of the economics of defect detection and removal to improve this understanding. The model is able to incorporate dynamic as well as static techniques in contrast to most other models of that kind. We especially analyse the model with state-ofthe-art sensitivity analysis methods to (1) identify the most relevant factors for model simplification and (2) prioritise the factors to guide further research and measurements.