SIMULATING EXOGENOUS SHOCKS IN COMPLEX SUPPLY NETWORKS USING MODULAR STOCHASTIC PETRI NETS

Almost all major companies are embedded in complex, global supply networks, consisting of multiple nested supply chains, and building up a high level of complexity. Exogenous shocks on these networks (e.g. natural disasters) can directly and indirectly impact companies and even cause their entire supply network to fail. However, today it is extremely difficult for a company to predict the actual impact of an exogenous shock on its supply network. Hence, companies are not able to identify adequate counteractive measures. Therefore safeguarding measures are oftentimes insufficient or even counterproductive. This paper deals with modelling, analyzing and quantifying impacts of exogenous shocks on supply networks using Petri Nets. It provides means to simulate the vulnerability of different network constellations regarding exogenous influences. In order to evaluate the proposed method, we simulate different intensities of an exogenous shock delaying the delivery for an exemplary supply network. We thereby illustrate which results could be yielded from a real-world application. For our exemplary network we find that the marginal effect of a disruption declines with an increasing intensity of shock. Moreover, the impact of shocks can be mitigated by appropriate counteractive measures like in this example by an increased safety margin of stock

Extra Functional Properties Evaluation of Self-managed Software Systems with Formal Methods

Multitud de aplicaciones software actuales están abocadas a operar en contextos dinámicos. Estos pueden manifestarse en términos de cambios en el entorno de ejecución de la aplicación, cambios en los requisitos de la aplicación, cambios en la carga de trabajo recibida por la aplicación, o cambios en cualquiera de los elementos que la aplicación software pueda percibir y verse afectada. Además, estos contextos dinámicos no están restringidos a un dominio particular de aplicaciones sino que se pueden encontrar en múltiples dominios, tales como: sistemas empotrados, arquitecturas orientadas a servicios, clusters para computación de altas prestaciones, dispositivos móviles o software para el funcionamiento de la red. La existencia de estas características disuade a los ingenieros de desarrollar software que no sea capaz de cambiar de modo alguno su ejecución para acomodarla al contexto en el que se está ejecutando el software en cada momento. Por lo tanto, con el objetivo de que el software pueda satisfacer sus requisitos en todo momento, este debe incluir mecanismos para poder cambiar su configuración de ejecución. Además, debido a que los cambios de contexto son frecuentes y afectan a múltiples dispositivos de la aplicación, la intervención humana que cambie manualmente la configuración del software no es una solución factible. Para enfrentarse a estos desafíos, la comunidad de Ingeniería del Software ha propuesto nuevos paradigmas que posibilitan el desarrollo de software que se enfrenta a contextos cambiantes de un modo automático; por ejemplo las propuestas Autonomic Computing y Self-* Software. En tales propuestas es el propio software quien gestiona sus mecanismos para cambiar la configuración de ejecución, sin requerir por lo tanto intervención humana alguna. Un aspecto esencial del software auto-adaptativo (Self-adaptive Software es uno de los términos más generales para referirse a Self-* Software) es el de planear sus cambios o adaptaciones. Los planes de adaptación determinan tanto el modo en el que se adaptará el software como los momentos oportunos para ejecutar tales adaptaciones. Hay un gran conjunto de situaciones para las cuales la propiedad de auto- adaptación es una solución. Una de esas situaciones es la de mantener al sistema satisfaciendo sus requisitos extra funcionales, tales como la calidad de servicio (Quality of Service, QoS) y su consumo de energía. Esta tesis ha investigado esa situación mediante el uso de métodos formales. Una de las contribuciones de esta tesis es la propuesta para asentar en una arquitectura software los sistemas que son auto-adaptativos respecto a su QoS y su consumo de energía. Con este objetivo, esta parte de la investigación la guía una arquitectura de tres capas de referencia para sistemas auto-adaptativos. La bondad del uso de una arquitectura de referencia es que muestra fácilmente los nuevos desafíos en el diseño de este tipo de sistemas. Naturalmente, la planificación de la adaptación es una de las actividades consideradas en la arquitectura. Otra de las contribuciones de la tesis es la propuesta de métodos para la creación de planes de adaptación. Los métodos formales juegan un rol esencial en esta actividad, ya que posibilitan el estudio de las propiedades extra funcionales de los sistemas en diferentes configuraciones. El método formal utilizado para estos análisis es el de las redes de Petri markovianas. Una vez que se ha creado el plan de adaptación, hemos investigado la utilización de los métodos formales para la evaluación de QoS y consumo de energía de los sistemas auto-adaptativos. Por lo tanto, se ha contribuido a la comunidad de análisis de QoS con el análisis de un nuevo y particularmente complejo tipo de sistemas software. Para llevar a cabo este análisis se requiere el modelado de los cambios din·micos del contexto de ejecución, para lo que se han utilizado una variedad de métodos formales, como los Markov modulated Poisson processes para estimar los parámetros de las variaciones en la carga de trabajo recibida por la aplicación, o los hidden Markov models para predecir el estado del entorno de ejecución. Estos modelos han sido usados junto a las redes de Petri para evaluar sistemas auto-adaptativos y obtener resultados sobre su QoS y consumo de energía. El trabajo de investigación anterior sacó a la luz el hecho de que la adaptabilidad de un sistema no es una propiedad tan fácilmente cuantificable como las propiedades de QoS -por ejemplo, el tiempo de respuesta- o el consumo de energÌa. En consecuencia, se ha investigado en esa dirección y, como resultado, otra de las contribuciones de esta tesis es la propuesta de un conjunto de métricas para la cuantificación de la propiedad de adaptabilidad de sistemas basados en servicios. Para conseguir las anteriores contribuciones se realiza un uso intensivo de modelos y transformaciones de modelos; tarea para la que se han seguido las mejores prácticas en el campo de investigación de la Ingeniería orientada a modelos (Model-driven Engineering, MDE). El trabajo de investigación de esta tesis en el campo MDE ha contribuido con: el aumento de la potencia de modelado de un lenguaje de modelado de software propuesto anteriormente y métodos de transformación desde dos lenguajes de modelado de software a redes de Petri estocasticas

Portability of Process-Aware and Service-Oriented Software: Evidence and Metrics

Modern software systems are becoming increasingly integrated and are required to operate over organizational boundaries through networks. The development of such distributed software systems has been shaped by the orthogonal trends of service-orientation and process-awareness. These trends put an emphasis on technological neutrality, loose coupling, independence from the execution platform, and location transparency. Execution platforms supporting these trends provide context and cross-cutting functionality to applications and are referred to as engines. Applications and engines interface via language standards. The engine implements a standard. If an application is implemented in conformance to this standard, it can be executed on the engine. A primary motivation for the usage of standards is the portability of applications. Portability, the ability to move software among different execution platforms without the necessity for full or partial reengineering, protects from vendor lock-in and enables application migration to newer engines. The arrival of cloud computing has made it easy to provision new and scalable execution platforms. To enable easy platform changes, existing international standards for implementing service-oriented and process-aware software name the portability of standardized artifacts as an important goal. Moreover, they provide platform-independent serialization formats that enable the portable implementation of applications. Nevertheless, practice shows that service-oriented and process-aware applications today are limited with respect to their portability. The reason for this is that engines rarely implement a complete standard, but leave out parts or differ in the interpretation of the standard. As a consequence, even applications that claim to be portable by conforming to a standard might not be so. This thesis contributes to the development of portable service-oriented and process-aware software in two ways: Firstly, it provides evidence for the existence of portability issues and the insufficiency of standards for guaranteeing software portability. Secondly, it derives and validates a novel measurement framework for quantifying portability. We present a methodology for benchmarking the conformance of engines to a language standard and implement it in a fully automated benchmarking tool. Several test suites of conformance tests for two different languages, the Web Services Business Process Execution Language 2.0 and the Business Process Model and Notation 2.0, allow to uncover a variety of standard conformance issues in existing engines. This provides evidence that the standard-based portability of applications is a real issue. Based on these results, this thesis derives a measurement framework for portability. The framework is aligned to the ISO/IEC Systems and software Quality Requirements and Evaluation method, the recent revision of the renowned ISO/IEC software quality model and measurement methodology. This quality model separates the software quality characteristic of portability into the subcharacteristics of installability, adaptability, and replaceability. Each of these characteristics forms one part of the measurement framework. This thesis targets each characteristic with a separate analysis, metrics derivation, evaluation, and validation. We discuss existing metrics from the body of literature and derive new extensions speciffically tailored to the evaluation of service-oriented and process-aware software. Proposed metrics are defined formally and validated theoretically using an informal and a formal validation framework. Furthermore, the computation of the metrics has been prototypically implemented. This implementation is used to evaluate metrics performance in experiments based on large scale software libraries obtained from public open source software repositories. In summary, this thesis provides evidence that contemporary standards and their implementations are not sufficient for enabling the portability of process-aware and service-oriented applications. Furthermore, it proposes, validates, and practically evaluates a framework for measuring portability

An adaptive service oriented architecture:Automatically solving interoperability problems

Organizations desire to be able to easily cooperate with other companies and still be flexible. The IT infrastructure used by these companies should facilitate these wishes. Service-Oriented Architecture (SOA) and Autonomic Computing (AC) were introduced in order to realize such an infrastructure, however both have their shortcomings and do not fulfil these wishes. This dissertation addresses these shortcomings and presents an approach for incorporating (self-) adaptive behavior in (Web) services. A conceptual foundation of adaptation is provided and SOA is extended to incorporate adaptive behavior, called Adaptive Service Oriented Architecture (ASOA). To demonstrate our conceptual framework, we implement it to address a crucial aspect of distributed systems, namely interoperability. In particular, we study the situation of a service orchestrator adapting itself to evolving service providers.

Feature-based generation of pervasive systems architectures utilizing software product line concepts

As the need for pervasive systems tends to increase and to dominate the computing discipline, software engineering approaches must evolve at a similar pace to facilitate the construction of such systems in an efficient manner. In this thesis, we provide a vision of a framework that will help in the construction of software product lines for pervasive systems by devising an approach to automatically generate architectures for this domain. Using this framework, designers of pervasive systems will be able to select a set of desired system features, and the framework will automatically generate architectures that support the presence of these features. Our approach will not compromise the quality of the architecture especially as we have verified that by comparing the generated architectures to those manually designed by human architects. As an initial step, and in order to determine the most commonly required features that comprise the widely most known pervasive systems, we surveyed more than fifty existing architectures for pervasive systems in various domains. We captured the most essential features along with the commonalities and variabilities between them. The features were categorized according to the domain and the environment that they target. Those categories are: General pervasive systems, domain-specific, privacy, bridging, fault-tolerance and context-awareness. We coupled the identified features with well-designed components, and connected the components based on the initial features selected by a system designer to generate an architecture. We evaluated our generated architectures against architectures designed by human architects. When metrics such as coupling, cohesion, complexity, reusability, adaptability, modularity, modifiability, packing density, and average interaction density were used to test our framework, our generated architectures were found comparable, if not better than the human generated architectures

Applications of Blockchain in Business Processes: A Comprehensive Review

Blockchain (BC), as an emerging technology, is revolutionizing Business Process Management (BPM) in multiple ways. The main adoption is to serve as a trusted infrastructure to guarantee the trust of collaborations among multiple partners in trustless environments. Especially, BC enables trust of information by using Distributed Ledger Technology (DLT). With the power of smart contracts, BC enforces the obligations of counterparties that transact in a business process (BP) by programming the contracts as transactions. This paper aims to study the state-of-the-art of BC technologies by (1) exploring its applications in BPM with the focus on how BC provides the trust of BPs in their lifecycles; (2) identifying the relations of BPM as the need and BC as the solution with the assessment towards BPM characteristics; (3) discussing the up-to-date progresses of critical BC in BPM; (4) identifying the challenges and research directions for future advancement in the domain. The main conclusions of our comprehensive review are (1) the study of adopting BC in BPM has attracted a great deal of attention that has been evidenced by a rapidly growing number of relevant articles. (2) The paradigms of BPM over Internet of Things (IoT) have been shifted from persistent to transient, from static to dynamic, and from centralized to decentralized, and new enabling technologies are highly demanded to fulfill some emerging functional requirements (FRs) at the stages of design, configuration, diagnosis, and evaluation of BPs in their lifecycles. (3) BC has been intensively studied and proven as a promising solution to assure the trustiness for both of business processes and their executions in decentralized BPM. (4) Most of the reported BC applications are at their primary stages, future research efforts are needed to meet the technical challenges involved in interoperation, determination of trusted entities, confirmation of time-sensitive execution, and support of irreversibility

Ecological interactions among important groundfishes in the Gulf of Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 2019Complex ecological interactions such as predation and competition play an important role in shaping the structure and function of marine communities. In fact, these processes can have greater impacts than those related to fishing. We assessed ecological interactions among economically important fishes in the Gulf of Alaska - a large marine ecosystem that has recently undergone considerable shifts in community composition. Specifically, we developed an index of predation for Walleye Pollock (Gadus chalcogrammus) to examine spatiotemporal changes in consumption, quantify portfolio effects, and better understand diversity-stability relationships within the demersal food web. We also evaluated the potential for competition between two important pollock predators, Arrowtooth Flounder (Atheresthes stomias) and Pacific Halibut (Hippoglossus stenolepis). We found highly variable predation intensity on Gulf of Alaska pollock. The combination of a single dominant predator and synchronous consumption dynamics indicated strong top-down control in the region. Spatial heterogeneity, however, may offset trophic instability at the basin scale. Assessments of resource partitioning provided little indication for competition between Arrowtooth Flounder and Pacific Halibut of similar lengths. Morphological differences between the two flatfish predators prompted an exploration into whether our conclusions about resource partitioning were dependent upon the size metric used. From this study, we found a relatively early onset of piscivory for Arrowtooth Flounder. Relationships between predator size and prey size also suggested gape limitation among Pacific Halibut sampled. Trophic niche separation was more pronounced for fishes with larger gapes, indicating greater potential for competition among smaller Arrowtooth Flounder and Pacific Halibut in Southeast Alaska. Reexamining basin-scale relationships between spatial and dietary overlap according to gape size would further elucidate the effects an increasing Arrowtooth Flounder population has had on changes in Pacific Halibut size-at-age. Results from this dissertation improve our understanding about the impacts of complex ecological interactions on population and community dynamics, and how those interactions may change in time, space, and under different environmental conditions.Pollock Conservation Cooperative Research Center (PCCRC; G00009488), Rasmuson Fisheries Research Cente

Numerical evaluation and analysis of the adhesion phenomena in thermal barrier coating systems through bio-mimicking plasma process

Thermal Barrier Coatings or TBCs when abbreviated are an imperative part of the thermal protection system of expensive equipment and machinery in the automobile and aeronautics industry. They provide protection to expensive alloy materials upto a temperature of 2700° C without expensive metallurgical additions. Unfortunately, the problem of coating adhesion has plagued the TBC field for years, leading to catastrophic failures in critical TBC systems. Efforts to chemically improve bond strength has not been entirely successful, so the only other efficient way to do this would be some kind of mechanical interlocking that occurs at micro/nano scales. This research work deals with the improvement of adhesion in TBC systems by numerical simulation and bench-marking of micro-geometric surface features that has been synthesized or reproduced in laboratory environment through electrochemical operations. For this, several geometries that benefit mechanical interlocking, and consequently improvements in mechanical \u27adhesion\u27 in TBCs has been compared. To simulate the mechanical and thermal loading on the micro geometries and to observe their effect, the commercial finite element software COMSOL was used. An analogy was drawn between the biological, Van der Waals dry adhesion mechanism in Gecko feet and that in the top surface of the thermally grown oxide (TGO) layer in TBC whereas the \u27mushroom head geometry\u27 in the Gecko feet provides improved adhesion (as much as 10 folds) compared to other geometries (spatular head, spherical head, or plain triangular crevices). An affordable synthesis process, termed “Electrolytic Plasma Processing (EPP) for recreating this specific geometry, is also proposed and its utility briefly entertained. The work ends with recommendations and suggestions for future works on this topic