Service-based systems that are dynamically composed at runtime to provide complex, adaptive functionality are currently one of the main development paradigms in software engineering. However, the Quality of Service (QoS) delivered by these systems remains an important concern, and needs to be managed in an equally adaptive and predictable way. To address this need, we introduce a novel, tool-supported framework for the development of adaptive service-based systems called QoSMOS (QoS Management and Optimization of Service-based systems). QoSMOS can be used to develop service-based systems that achieve their QoS requirements through dynamically adapting to changes in the system state, environment, and workload. QoSMOS service-based systems translate high-level QoS requirements specified by their administrators into probabilistic temporal logic formulae, which are then formally and automatically analyzed to identify and enforce optimal system configurations. The QoSMOS self-adaptation mechanism can handle reliability and performance-related QoS requirements, and can be integrated into newly developed solutions or legacy systems. The effectiveness and scalability of the approach are validated using simulations and a set of experiments based on an implementation of an adaptive service-based system for remote medical assistance.

https://hal.inria.fr/hal-00663216/document

Dynamic QoS Management and Optimization in Service-Based Systems

A framework for QoS-aware binding and re-binding of composite web services

Due to significant industrial demands toward software systems with increasing complexity and challenging quality requirements, software architecture design has become an important development activity and the research domain is rapidly evolving. In the last decades, software architecture optimization methods, which aim to automate the search for an optimal architecture design with respect to a (set of) quality attribute(s), have proliferated. However, the reported results are fragmented over different research communities, multiple system domains, and multiple quality attributes. To integrate the existing research results, we have performed a systematic literature review and analyzed the results of 188 research papers from the different research communities. Based on this survey, a taxonomy has been created which is used to classify the existing research. Furthermore, the systematic analysis of the research literature provided in this review aims to help the research community in consolidating the existing research efforts and deriving a research agenda for future developments.

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Software Architecture Optimization Methods: A Systematic Literature Review

Software architecture optimization methods: A systematic literature review

Service compositions build new services by orchestrating a set of existing services. In the Internet of Services there may be many functional similar services, but with different Quality of Service (QoS). Thus a significant research problem in service compositions is how to select the composition’s composite services that the overall QoS of the composition is being maximized. This paper summarizes, classifies and evaluates major research efforts in this area and gives an overview about further open research questions.

QoS-Aware Service Composition: A Survey

This paper discusses the Quality of Service (QoS)- aware composition of Web Services. The work is based on the assumption that for each task in a workflow a set of alternative Web Services with similar functionality is available and that these Web Services have different QoS parameters and costs. This leads to the general optimization problem of how to select Web Services for each task so that the overall QoS and cost requirements of the composition are satisfied. Current proposals use exact algorithms or complex heuristics (e.g. genetic algorithms) to solve this problem. An actual implementation of a workflow engine (like our WSQoSX architecture), however, has to be able to solve these optimization problems in real-time and under heavy load. Therefore, we present a heuristic that performs extremely well while providing excellent (almost optimal) solutions. Using simulations, we show that in most cases our heuristic is able to calculate solutions that come as close as 99% to the optimal solution while taking less than 2% of the time of a standard exact algorithm. Further, we also investigate how much and under which circumstances the solution obtained by our heuristic can be further improved by other heuristics.

Heuristics for QoS-aware Web Service Composition

The composition of Web Services to workflows is one of the major challenges in the area of service-oriented computing. To meet the business and user requirements, it is crucial to manage the quality of service (QoS) of Web Service workflows. In our approach, we calculate the execution plan of workflows on the QoS attributes ex ante based on predictions. However, due to the volatile nature of the Internet and the web servers, the runtime behavior of Web Services is likely to differ from the predictions. Therefore, we propose replanning as a mechanism to adapt the execution plan to the actual behavior of already executed services by a dynamic service selection at runtime, ensuring that the QoS and cost requirements will still be met. In this paper, we discuss replanning strategies, show how replanning leads to cost-savings in most cases, and evaluate the additional overhead caused by the adaptation of the execution plan at runtime.

Dynamic Replanning of Web Service Workflows

The dynamic composition of Web Services to workflows at runtime is a major challenge in the emerging field of Serviceoriented computing. At this, preferences and constraints defined by the user have to be considered, e.g. executing a workflow with the cheapest Web Services, but not exceeding a given execution time. Due to the volatile nature of the Web Service environment the actual runtime behavior of Web Services may deviate from the one estimated in the planning phase. Thus, replanning mechanisms are crucial for adapting a workflow to the real behavior ensuring that its execution remains feasible, valid and optimal subject to the preferences and constraints defined by the user. Replanning mechanisms have to perform in real-time not to create further delay to the workflow execution. Thus, in this paper, we introduce a heuristic based replanning mechanism.

An Approach for Replanning of Web Service Workflows

Web Services as a technology to enable distributed business processes gain in importance, especially in the area of Enterprise Application Integration (EAI) and Business Process Outsourcing (BPO). However, the support of Quality of Service (QoS) is crucial in this context. Without any guarantee regarding QoS, no enterprise is willing to rely on external Web Services within critical business processes. Thus, we designed and implemented the Web Service Quality of Service Architectural Extension (WSQoSX)as an integrated Web Service system with comprehensive QoS support [2, 4]. WSQoSX supports the assessment of Web Services to assure that only Web Services will be used in critical business processes that satisfy the requirements defined by the user. The selection and execution of a certain Web Service depends on its QoS-properties described by a Service Level Agreements (SLAs) document. The compliance with given SLAs is monitored by WSQoSX as well. In case of a Web Service not being able to fulfil the requirements, it can be replaced during runtime by selecting an alternative Web Service out of a pool of similar Web Services. Additionally, providers can register their Web Service offerings using the same Web-based interface, making WSQoSX a marketplace for Web Services.

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WSQoSX --- A QoS Architecture for Web Service Workflows

Im Zusammenhang mit der unternehmensubergreifenden Integration externer Partner in Geschaftsprozesse, haben serviceorientierte Architekturen zunehmend an Bedeutung gewonnen. Mit zunehmender Existenz von Servicen gleicher oder ahnlicher Funktionalitat steigt die Relevanz nichtfunktionaler Eigenschaften als Selektionskriterium bei der Serviceauswahl. Geschaftsprozesse derart automatisiert aus Servicen zu orchestrieren, dass hierbei definierte Praferenzen und Restriktionen hinsichtlich ihrer nicht-funktionalen Eigenschaften bestmoglich erfullt werden, fuhrt zu einem Kompositionsproblem, welches sich als NP-schweres Optimierungsproblem formulieren lasst. Gegenstand dieses Beitrages ist die Vorstellung eines heuristischen Verfahrens zur Losung des Service-Kompositionsproblems, welches mit geringer Laufzeit nahezu optimale Losungen erzeugt, sowie gut mit der Problemgrose skaliert. Aufgrund der hohen Performanz eignet sich das Verfahren in besonderem Mase fur zeitkritische Anwendungen.

Michael Spahn

Papers

Heuristics for QoS-aware Web Service Composition

Dynamic Replanning of Web Service Workflows

An Approach for Replanning of Web Service Workflows

WSQoSX --- A QoS Architecture for Web Service Workflows

Ein heuristisches Verfahren zur dienstgütebasierten Optimierung flexibler Geschäftsprozesse