Julian Eckert

Cost-Driven Optimization of Complex Service-Based Workflows for Stochastic QoS Parameters

The challenge of optimally selecting services from a set of functionally appropriate ones under Quality of Service (QoS) constraints -- the Service Selection Problem -- has been extensively addressed in the literature based on deterministic parameters. In practice, however, Quality of Service QoS parameters rather follow a stochastic distribution. In the work at hand, we present an integrated approach which addresses the Service Selection Problem for complex workflows in conjunction with stochastic Quality of Service parameters. Accounting for penalty cost which accrue due to Quality of Service violations, our approach reduces the impact of stochastic QoS behavior on total cost significantly.

Towards automated monitoring and alignment of service-based workflows

Using Web services and service-oriented architectures to implement cross-organizational workflows has become state-of-the-art for the realization of collaborations between enterprises. Here, a key issue is the monitoring of workflows and services based on given business requirements and the handling of deviations from those requirements to fulfil service level agreements. In this paper we present an approach to the automated monitoring and alignment of service-based workflows. We describe a policy language for the specification of requirements and deviation handling as well as a distributed architecture supporting automated monitoring and alignment in service ecosystems.

LOG4SWS.KOM: Self-Adapting Semantic Web Service Discovery for SAWSDL

In recent years, a number of approaches to semantic Web service matchmaking have been proposed. Most of these proposals are based on discrete and thus relatively coarse Degrees of Match (DoMs). However, different basic assumptions regarding the generalization and specialization of semantic concepts in ontologies and their subsequent rating in matchmaking exist. Hence, most matchmakers are only properly suitable if these assumptions are met. In this paper, we present an approach for mapping subsumption reasoning-based DoMs to a continuous scale. Instead of determining the numerical equivalents of the formerly discrete DoMs manually, these values are automatically derived using a linear regression model. This permits not only easy combination with other numerical similarity measures, but also allows to adapt matchmaking to different basic assumptions. These notions are implemented and tested in LOG4SWS.KOM -- a matchmaker for SAWSDL that provides very good evaluation results with respect to Information Retrieval metrics such as precision and recall.

Resource Planning Heuristics for Service-Oriented Workflows

Resource allocation and resource planning, especially in a SOA and grid environment, become crucial. Particularly, in an environment with a huge number of workflow consumers requesting a decentralized cross-organizational workflow, performance evaluation and execution-management of service-oriented workflows gain in importance. The need for an effective and efficient workflow management forces enterprises to use intelligent optimization models and heuristics to compose workflows out of several services under real-time conditions. This paper introduces the required architecture workflow performance extension - WPX.KOM for resource planning and workload prediction purposes. Furthermore, optimization approaches and a high-performance heuristic solving the addressed resource planning problem with low computational overhead are presented.

QoS-Aware Service Composition for Complex Workflows

In Service-oriented Architectures, business processes are realized by composing loosely coupled services. With the ongoing success of Web services technologies, the invocation of Web services goes beyond enterprises’ borders. So, besides implementing required services within one enterprise, services can be purchased from external service providers. With a growing number and variety of services, enterprises can choose between functionally equivalent services at different cost and quality levels. The paper at hand addresses this service selection problem considering complex workflow patterns. Aggregation functions for different quality of service parameters are proposed and a linear optimization problem is formulated, which can be solved using integer linear programming techniques or by applying heuristic solutions.

Worst-Case Workflow Performance Optimization

Performance evaluation and execution management of service-oriented workflows became quite important in order to avoid performance degradation. Performance measurement is crucial to ensure that workflow execution remains feasible and that SLA violations due to overload are avoided. Network calculus as a well-known system theory for deterministic queuing systems can be used to describe the worst-case performance behavior of a workflow in order to plan workflow control in advance. Concerning business processes with high repetition rates the workflow controller has to be able to serve all incoming requests with an optimal composition of Web services. Thus, this paper presents a formal worst-case calculation model using the concepts of network calculus. Furthermore, optimization problems based on the worst-case scenario are introduced in order to minimize the worst-case delay and to maximize the throughput of the Web services invoked with minimal costs.

Process reliability in service oriented architectures

The creation of business processes by composing Web services has attracted considerable efforts with respect to integrating elements of Service Oriented Architectures within enterprise applications. If one of those atomic services fails, the whole business process does not necessarily have to fail, too, as it is possible to exchange the faulty service during runtime with another one which has the same functionality. In this paper we present a service monitoring and exchanging approach that aims to ensure a successful execution of crucial processes in case of faulty services. It consists of three parts which supervise the process execution and try to recover it if an error occurs. In case process reliability is not fore grounded, our approach can also serve as basis for process optimization.

An approach to evaluate and enhance the retrieval of Semantic Web services

In order to achieve the (semi-) automatic composition of Web services to business processes and workflows respectively, it is necessary to make use of semantic information regarding the capabilities and further characteristics of particular Web services. In recent years, a couple of approaches have been proposed to achieve (semi-) automatic annotation, retrieval, and composition of Semantic Web services; however, differences in Web service standards and repositories used for the evaluation of these approaches lead to a lack of both in-depth evaluations and comparability of the proposals. In this paper, we present a workbench to test and evaluate the performance of annotation, retrieval, and composition algorithms for Semantic Web services. As a proof of concept we introduce SEM.KOM, a prototypical implementation based on standardized Web service technologies.

QoS-Based Optimization of Service Compositions for Complex Workflows

In Service-oriented Architectures, business processes can be realized by composing loosely coupled services. If services in the Internet of Services with comparable functionalities but varying quality levels are available at different costs on service marketplaces, service requesters can decide, which services from which service providers to select. The work at hand addresses computing an optimal solution to this service-selection-problem considering complex workflow patterns. For this, a linear optimization problem is formulated, which can be solved by applying integer linear programming techniques.

Study and Comparison of Adaptation Mechanisms for Performance Enhancements of Mobile Web Service Consumption

Mobile Web services lie on the intersection of two big IT trends, namely Service-oriented Architectures (SOA) and mobile applications. So, their usage is likely to expand dramatically in the next years. However, the heavyweight nature of service-orientation in terms of the messaging-overhead that is necessary in order to achieve interoperability and loose-coupling comes in contrast with the lightweight nature of mobile devices and with the need to transmit wirelessly as few data as possible. This study categorizes the mechanisms that have been designed in order to bridge this gap, provides comparisons, discusses the results of related experiments, and introduces the future scenario in which the insights of the study can be exploited.