141 research outputs found
A Framework for QoS-aware Execution of Workflows over the Cloud
The Cloud Computing paradigm is providing system architects with a new
powerful tool for building scalable applications. Clouds allow allocation of
resources on a "pay-as-you-go" model, so that additional resources can be
requested during peak loads and released after that. However, this flexibility
asks for appropriate dynamic reconfiguration strategies. In this paper we
describe SAVER (qoS-Aware workflows oVER the Cloud), a QoS-aware algorithm for
executing workflows involving Web Services hosted in a Cloud environment. SAVER
allows execution of arbitrary workflows subject to response time constraints.
SAVER uses a passive monitor to identify workload fluctuations based on the
observed system response time. The information collected by the monitor is used
by a planner component to identify the minimum number of instances of each Web
Service which should be allocated in order to satisfy the response time
constraint. SAVER uses a simple Queueing Network (QN) model to identify the
optimal resource allocation. Specifically, the QN model is used to identify
bottlenecks, and predict the system performance as Cloud resources are
allocated or released. The parameters used to evaluate the model are those
collected by the monitor, which means that SAVER does not require any
particular knowledge of the Web Services and workflows being executed. Our
approach has been validated through numerical simulations, whose results are
reported in this paper
A conceptual and architectural characterization of antifragile systems
Antifragility is one of the terms that have recently emerged with the aim of indicating a direction that should be pursued toward the objective of designing Information and Communications Technology systems that remain trustworthy despite their dynamic and evolving operating context. We present a characterization of antifragility, aiming to clarify from a conceptual viewpoint the implications of its adoption as a design guideline and its relationships with other approaches sharing a similar objective. To this end, we discuss the inclusion of antifragility (and related concepts) within the well-known dependability taxonomy, which was proposed a few decades ago with the goal of providing a reference framework to reason about the different facets of the general concern of designing dependable systems. From our conceptual characterization, we then derive a possible path toward the engineering of antifragile systems
Uncertainty in coupled models of cyber-physical systems
The development of cyber-physical systems typically involves the association between multiple coupled models that capture different aspects of the system and the environment where it operates. Due to the dynamic aspect of the environment, unexpected conditions and uncertainty may impact the system. In this work, we tackle this problem and propose a taxonomy for characterizing uncertainty in coupled models. Our taxonomy extends existing proposals to cope with the particularities of coupled models in cyber-physical systems. In addition, our taxonomy discusses the notion of uncertainty propagation to other parts of the system. This allows for studying and (in some cases) quantifying the effects of uncertainty on other models in a system even at design time. We show the applicability of our uncertainty taxonomy in real use cases motivated by our envisioned scenario of automotive development
Software engineering for self-adaptive systems:research challenges in the provision of assurances
The important concern for modern software systems is to become more cost-effective, while being versatile, flexible, resilient, dependable, energy-efficient, customisable, configurable and self-optimising when reacting to run-time changes that may occur within the system itself, its environment or requirements. One of the most promising approaches to achieving such properties is to equip software systems with self-managing capabilities using self-adaptation mechanisms. Despite recent advances in this area, one key aspect of self-adaptive systems that remains to be tackled in depth is the provision of assurances, i.e., the collection, analysis and synthesis of evidence that the system satisfies its stated functional and non-functional requirements during its operation in the presence of self-adaptation. The provision of assurances for self-adaptive systems is challenging since run-time changes introduce a high degree of uncertainty. This paper on research challenges complements previous roadmap papers on software engineering for self-adaptive systems covering a different set of topics, which are related to assurances, namely, perpetual assurances, composition and decomposition of assurances, and assurances obtained from control theory. This research challenges paper is one of the many results of the Dagstuhl Seminar 13511 on Software Engineering for Self-Adaptive Systems: Assurances which took place in December 2013
Software Engineering for Self-Adaptive Systems: A second Research Roadmap
The goal of this roadmap paper is to summarize the state of-the-art and identify research challenges when developing, deploying and managing self-adaptive software systems. Instead of dealing with a wide range of topics associated with the field, we focus on four essential topics of self-adaptation:
design space for adaptive solutions, processes, from centralized to decentralized control, and practical run-time verification and validation. For each topic, we present an overview, suggest future directions, and focus on selected challenges. This paper complements and extends a previous roadmap
on software engineering for self-adaptive systems published in 2009 covering a different set of topics, and reflecting in part on the previous paper. This roadmap is one of the many results of the Dagstuhl Seminar 10431 on Software
Engineering for Self-Adaptive Systems, which took place in October 2010
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