Virtualization promises to reduce data centers' total cost of ownership by enabling the creation of a small set of standardized building blocks to be shared and used many times indifferent software stacks. However, without proper methodology and tools, an organization can easily end up with a large number of one-off virtual images, adversely affecting the cost. We propose an approach, tool, and algorithms for constructing high-quality, semantically-rich image building blocks that are easy to share, compose, and reuse. In our approach, domain experts codify knowledge of a particular software product (or a combination thereof) in a platform- and cloud-agnostic software bundle. Image builders easily construct virtual images by composing a set of standardized bundles. Semantic-based validation guarantees a valid and complete image design. Moreover, we propose algorithms to automate image design by searching for an optimal set of building blocks taking into account multiple metrics such as cost, size, and expected build duration.

We propose a domain-specific service selection mechanism and system implementation to address the issue of runtime adaptation of composite services that implement mission-critical business processes. To this end, we leverage quality of service (QoS) as a means to specify rigid dependability requirements. QoS does not include only common attributes such as availability or response time but also attributes specific to certain business domains and processes. Therefore, we combine both domain-agnostic and domain-specific QoS attributes in an adaptive QoS model. For specifying the service selection strategy, we propose a domain-specific language called VieDASSL to specify so-called selectors. This language can be used to specify selector implementations based on the available QoS attributes. Both the QoS model implementation and the selectors can be adapted at runtime to deal with changing business and QoS requirements. Our approach is implemented on top of an existing WS-BPEL engine. We demonstrate its feasibility by implementing a case study from the telecommunication domain.

In this work we construct partial order plans from a pool of atomic services described in OWL-S. We make extensions to Partial Order Planning to allow multiple conditional effects in action definitions. The purpose is to handle the uncertain behavior of Web services with incomplete initial information. We post-process the partial order plan to auto-generate a workflow model. We developed a method to identify a subset of workflow patterns from the solution plan to create a workflow diagram.

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 provider's SLAs. We explain PREvent in detail and show the impact on SLA violations based on a case study.

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.

Since the Internet of Services (IoS) is becoming reality, there is an inherent need for novel service selection mechanisms, which work in spite of large numbers of alternative services and take the user-centric nature of services in the IoS into account. One way to do this is to incorporate feedback from previous service users. However, practical issues such as trust aspects, interaction contexts or synonymous feedbacks have to be taken into account. In this paper we discuss a service selection mechanism which makes use of structured and unstructured feedback to capture the Quality of Experience that services have provided in the past. We have implemented our approach within the SOA runtime VRESCO, where we use freeform tags for unstructured and numerical ratings for structured user feedback. We discuss the general process of feedback-based service selection, and explain how the problems described above can be tackled. We conclude the paper with an illustrative case study and discussion of the presented ideas.

A simple and effective composition of software services into higher-level composite services is still a very challenging task. Especially in enterprise environments, quality of service (QoS) concerns play a major role when building software systems following the service-oriented architecture (SOA) paradigm. Inthis paper we present a composition approach based on a domain-specific language(DSL) for specifying functional requirements of services and the expected QoS inform of constraint hierarchies by leveraging hard and soft constraints. Acomposition runtime will resolve the user's constraints to find an optimize dcomposition semi-automatically. To this end we leverage data flow analysis to generate a structured composition model and use two different techniques for the optimization, a constraint programming and an integer programming approach.

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.

Software as a Service (SaaS) and the possibility to compose Web services provisioned over the Internet are important assets for a service-oriented architecture (SOA). However, the complexity and time for developing and provisioning a composite service is very high and it is generally an error-prone task. In this paper we address these issues by describing a semi-automated "Composition as a Service'' (CaaS) approach combined with a domain-specific language called VCL (Vienna composition language). The proposed approach facilitates rapid development and provisioning of composite services by specifying what to compose in a constraint-hierarchy based way using VCL. Invoking the composition service triggers the composition process and upon success the newly composed service is immediately deployed and available. This solution requires no client-side composition infrastructure because it is transparently encapsulated in the CaaS infrastructure.

In general, provenance of electronic data represents an important issue in information systems. So far, service-oriented computing research has mainly focused on provenance of data. However, service provenance also plays a central role since service providers and consumers want to be aware of the service's origin and history. In this paper, we present an approach for service provenance that builds on service metadata and various service runtime events. In addition, access control mechanisms are implemented to restrict access to this information. Besides being able to query and subscribe to provenance information, provenance graphs can be used to illustrate the history of services. We give some usage examples of service provenance and show how our approach was integrated into the VRESCo Web service runtime environment.

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 user's 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.

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.

Developing cross-organizational business processes is a tedious task. The partners have to agree on a common data format and meaning as well as on the Quality of Service (QoS) requirements each partner has to fulfill. The QoS requirements are typically described using Service Level Agreements (SLAs) among the partners. In this paper, we propose a top-down modeling approach for Web service based business processes to capture the functional and non-functional aspects using a choreography language (WS-CDL) which describes the message interactions among the participants. The choreography is annotated with SLAs for the different partners. For each partner in the process, an orchestration (in WS-BPEL) and the necessary Web service templates are automatically generated. Additionally, the Service Level Objectives (SLOs) from the partner SLAs are automatically translated into policies which can then be enforced by a BPEL engine during execution.

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.

Business rules provide an elegant solution to manage dynamic business logic by separating business knowledge from its implementation logic. The drawback of most existing business rule approaches is the lack of standardization and interoperability. The lack of service-orientation and remote accessibility of business rule engines makes it hard to use business rules in distributed environments. This paper contributes the design and implementation of ViDRE (Vienna distributed rules engine), a service-oriented business rule engine based on RuleML. ViDRE enables enterprise applications to access business rules as easy as accessing a database, by exposing rules as Web services. ViDRE uses RuleML as an interlingua to represent facts, rules, and queries. One of the main contributions of the ViDRE approach is the ability to distribute rules and facts across various rule engines, therefore, enabling powerful ways of separating and executing business rules within intra- and interorganizational boundaries

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