Florian Rosenberg

A survey on context-aware systems

Context-aware systems offer entirely new opportunities for application developers and for end users by gathering context data and adapting systems behaviour accordingly. Especially in combination with mobile devices, these mechanisms are of high value and are used to increase usability tremendously. In this paper, we present common architecture principles of context-aware systems and derive a layered conceptual design framework to explain the different elements common to most context-aware architectures. Based on these design principles, we introduce various existing context-aware systems focusing on context-aware middleware and frameworks, which ease the development of context-aware applications. We discuss various approaches and analyse important aspects in context-aware computing on the basis of the presented systems.

Non-intrusive monitoring and service adaptation for WS-BPEL

Web service processes currently lack monitoring and dynamic (runtime) adaptation mechanisms. In highly dynamic processes, services frequently need to be exchanged due to a variety of reasons. In this paper we present VieDAME, a system which allows monitoring of BPEL processes according to Quality of Service (QoS) attributes and replacement of existing partner services based on various (pluggable) replacement strategies. The chosen replacement services can be syntactically or semantically equivalent to the BPEL interface. Services can be automatically replaced during runtime without any downtime of the overall system. We implemented our solution with an aspect-oriented approach by intercepting SOAP messages and allow services to be exchanged during runtime with little performance penalty costs, as shown in our experiments, thereby making our approach suitable for high-availability BPEL environments.

Bootstrapping Performance and Dependability Attributes ofWeb Services

Web services gain momentum for developing flexible service-oriented architectures. Quality of service (QoS) issues are not part of the Web service standard stack, although non-functional attributes like performance, dependability or cost and payment play an important role for service discovery, selection, and composition. A lot of research is dedicated to different QoS models, at the same time omitting a way to specify how QoS parameters (esp. the performance related aspects) are assessed, evaluated and constantly monitored. Our contribution in this paper comprises: a) an evaluation approach for QoS attributes of Web services, which works completely service-and provider independent, b) a method to analyze Web service interactions by using our evaluation tool and extract important QoS information without any knowledge about the service implementation. Furthermore, our implementation allows assessing performance specific values (such as latency or service processing time) that usually require access to the server which hosts the service. The result of the evaluation process can be used to enrich existing Web service descriptions with a set of up-to-date QoS attributes, therefore, making it a valuable instrument for Web service selection

Monitoring, Prediction and Prevention of SLA Violations in Composite Services

We propose the PREvent framework, which is a system that integrates event-based monitoring, prediction of SLA violations using machine learning techniques, and automated runtime prevention of those violations by triggering adaptation actions in service compositions. PREvent improves on related work in that it can be used to prevent violations ex ante, before they have negatively impacted the providers SLAs. We explain PREvent in detail and show the impact on SLA violations based on a case study.

Business rules integration in BPEL - a service-oriented approach

Business rules change quite often. These changes cannot be handled efficiently by representing business rules embedded in the source code of the business logic. Efficient handling of rules that govern ones business is one factor for success. That is where business rules engines play an important role. The service-oriented computing paradigm is becoming more and more popular. Services offered by different providers, are composed to new services by using Web service composition languages such as BPEL. Such process-based composition languages lack the ability to use business rules managed by different business rules engines in the composition process. In this paper, we propose an approach on how to use and integrate business rules in a service-oriented way into BPEL.

A context-based mediation approach to compose semantic Web services

Web services composition is a keystone in the development of interoperable systems. However, despite the widespread adoption of Web services, several obstacles still hinder their smooth automatic semantic reconciliation when being composed. Consistent understanding of data exchanged between composed Web services is hampered by various implicit modeling assumptions and representations. Our contribution in this article revolves around context and how it enriches data exchange between Web services. In particular, a context-based mediation approach to solve semantic heterogeneities between composed Web services is presented.

Composing RESTful Services and Collaborative Workflows: A Lightweight Approach

The use of RESTful Web services has gained momentum in the development of distributed applications based on traditional Web standards such as HTTP. In particular, these services can integrate easily into various applications, such as mashups. Composing RESTful services into Web-scale workflows requires a lightweight composition language thats capable of describing both the control and data flow that constitute a workflow. The authors address these issues with Bite, a lightweight and extensible composition language that enables the creation of Web-scale workflows and uses RESTful services as its main composable entities.

End-to-End Support for QoS-Aware Service Selection, Binding, and Mediation in VRESCo

Service-Oriented Computing has recently received a lot of attention from both academia and industry. However, current service-oriented solutions are often not as dynamic and adaptable as intended because the publish-find-bind-execute cycle of the Service-Oriented Architecture triangle is not entirely realized. In this paper, we highlight some issues of current web service technologies, with a special emphasis on service metadata, Quality of Service, service querying, dynamic binding, and service mediation. Then, we present the Vienna Runtime Environment for Service-Oriented Computing (VRESCo) that addresses these issues. We give a detailed description of the different aspects by focusing on service querying and service mediation. Finally, we present a performance evaluation of the different components, together with an end-to-end evaluation to show the applicability and usefulness of our system.

Web service clustering using multidimensional angles as proximity measures

Increasingly, application developers seek the ability to search for existing Web services within large Internet-based repositories. The goal is to retrieve services that match the users requirements. With the growing number of services in the repositories and the challenges of quickly finding the right ones, the need for clustering related services becomes evident to enhance search engine results with a list of similar services for each hit. In this article, a statistical clustering approach is presented that enhances an existing distributed vector space search engine for Web services with the possibility of dynamically calculating clusters of similar services for each hit in the list found by the search engine. The focus is laid on a very efficient and scalable clustering implementation that can handle very large service repositories. The evaluation with a large service repository demonstrates the feasibility and performance of the approach.

Monitoring and Analyzing Influential Factors of Business Process Performance

Business activity monitoring enables continuous observation of key performance indicators (KPIs). However, if things go wrong, a deeper analysis of process performance becomes necessary. Business analysts want to learn about the factors that influence the performance of business processes and most often contribute to the violation of KPI target values, and how they relate to each other. We provide a framework for performance monitoring and analysis of WS-BPEL processes, which consolidates process events and Quality of Service measurements. The framework uses machine learning techniques in order to construct tree structures, which represent the dependencies of a KPI on process and QoS metrics. These dependency trees allow business analysts to analyze how the process KPIs depend on lower-level process metrics and QoS characterisitics of the IT infrastructure. Deeper knowledge about the structure of dependencies can be gained by drill-down analysis of single factors of influence.