Xiaoqiang Qiao

Web services composition: A decade's overview

Service-oriented computing (SOC) represents a paradigm for building distributed computing applications over the Internet. In the past decade, Web services composition has been an active area of research and development endeavors for application integration and interoperation. Although Web services composition has been heavily investigated, several issues related to dependability, ubiquity, personalization, among others, still need to be addressed, especially giving the recent rise of several new computing paradigms such as Cloud computing, social computing, and Web of Things. This article overviews the life cycle of Web services composition and surveys the main standards, research prototypes, and platforms. These standards, research prototypes, and platforms are assessed using a set of assessment criteria identified in the article. The paper also outlines several research opportunities and challenges for Web services composition.

Developing a Concurrent Service Orchestration Engine Based on Event-Driven Architecture

WS-BPEL (BPEL for short) represents the de-factor standard for the Web services composition. Service orchestration engines, also named BPEL engines, are in charge of executing and managing the workflow specified in BPEL. As a kind of server application, high performance under massive concurrency is necessary to design a scalable BPEL engine, and it is a challenging problem to implement a correct and highly concurrent BPEL engine. We propose an approach based on event-driven architecture to design BPEL engine and introduce the FSM (finite state machines) to describe the semantics of the BPEL process. We also test our BPEL engine and prove the improvement in capability of handling the massive concurrency comparing to the one based on the thread-based concurrent paradigm.

A Two-Level Virtual Machine Self-Reconfiguration Mechanism for the Cloud Computing Platforms

Cloud computing is a new model and technology that leverage the efficient pooling of on-demand, self-managed virtual infrastructure. Virtualization packages the applications in the form of Virtual Machine (VM) and provides significant benefits by reconfiguring the VMs dynamically. VM reconfiguration is hard and complicated, and existing work addressed the problem with diverse objectives by answering the questions of when to reconfigure, which VMs should be reconfigured and where to host the VMs. However, we found that the runtime reconfiguration affects the total costs significantly. Then we propose a two-level runtime reconfiguration mechanism to automate the operations with the objective of minimizing the costs. The mechanism includes the local adjustment and the parallel migration. Employing the local adjustment, VMs on a same server can be reconfigured in a time-division multiplexed way based on the load trend prediction, which can avoid the unnecessary VM migrations. Nevertheless, VM migration is inevitable when the server is overloaded. Considering the conflict between reducing the migration cost and minimizing the performance interference, we propose a VM parallel migration strategy and map it to the max matching problem of the bipartite graph. We implement a framework based on Xen and evaluate the mechanism with a preliminary experiment. The results show that this two-level self-reconfiguration mechanism is effective in reducing the VM runtime reconfiguration costs.

Implementing Service Collaboration Based on Decentralized Mediation

Service collaboration allows the realization of more complicated business logic by using existing services. As Web services are generally designed by different organizations, there will be certain mismatches that make them not fit together. Mediation mechanism plays an important role in service collaboration, which guarantees the seamless interaction without changing the internal implementation of services. This paper proposes a comprehensive approach of decentralized mediation framework for multiple services collaboration across organizational boundaries. We also present a novel technique for mediation existence checking and mediator synthesis based on interaction paths, which not only reduces the complexity of mediator synthesis but also provides parallel sub-processes for multiple interactive parts to ensure the parallelism degree of the mediator.

Implementing Dynamic Management for Mediated Service Interactions

Considering the inherent heterogeneous, autonomous and dynamic nature of Web services, mismatches usually exist between service signatures and behaviors, and mediation is a common approach for service interactions. Current techniques focus on mismatch analysis and automatic synthesis of mediators at development time, but they do not consider the effect that dynamic changes of services bring about for mediators at runtime. Since Web services are continuously evolving, mediators should be equipped with the dynamic adaptation and re-configuration capabilities to avoid being the bottleneck of the adaptability of service interactions. To address this challenge we propose a dynamic management approach for mediated service interactions. In this paper, migration strategies and correctness criteria suitable for the mediator are provided to realize dynamic adjustment of mediators at runtime, which ensures the agility and adaptability of service interactions based on the mediation mechanism.

Handling Irreconcilable Mismatches in Web Services Mediation

Service mediation provides an effective way to integrate a service requester and a service provider, by reconciling the mismatches between the two. The techniques to assess the mediation degrees of services, to analyze irreconcilable mismatches, and to provide resolutions for irreconcilable behavioral mismatches are therefore essential. To address these challenges, we introduce in this paper two quantifiable metrics, called service mediatability and modification complexity, to evaluate the feasibility and complexity of mediating a requester and a service. We also propose a pattern-based approach for analyzing service behaviors that cannot be automatically mediated. We further offer resolutions for each irreconcilable mismatch pattern, which help developers to adjust and improve the service behaviors to fulfill the interaction requirements.

Detecting Inter-Component Configuration Errors in Proactive: A Relation-Aware Method

Configuration errors, similar to bugs, are often the dominant causes of errors in deployed applications, leading to application failures, exceptions and even crashes. Misconfigurations are hard to detect and diagnose. To address this issue, we propose a method to detect the potential misconfigurations. Unlike the existing work, we focus on the misconfigurations introduced by the relations between components. The options in configuration files of an application are extracted and classified into several groups. Directed by the relations, the possible inter-related parameters are discovered and checked with some proposed checking rules. We implement a prototype and make evaluations. The case study shows that this method can detect and check a majority of inter-related configuration options with less human effort.

A Virtual Machine Placement and Reconfiguration Framework for Cloud Computing Platforms

As a rising application paradigm and technology, cloud computing can leverage the efficient pooling of on-demand, self-managed virtual infrastructure. How to maximize the resource utilization and how to reduce the cost of configuration are essential issues in cloud computing. In this paper, the authors propose a framework to achieve these objectives by optimizing VM placement and deciding when and how to perform the VM reconfigurations. The authors leverage the vector arithmetic to model the objective of balancing the multiple resource utilization and propose an optimization method for the static VM placement. Then the authors propose a two-level runtime reconfiguration policy, including the local adjustment and the parallel migration, to minimize the reconfiguration cost. Finally, the authors implement a prototype to validate and evaluate the proposed mechanism with a set of preliminary experiments, which shows that our work can maximize the resource utilization while effectively reducing the cost of the runtime reconfiguration.

A Decentralized Approach for Inter-Enterprise Business Process Collaboration

Chinese Acad Sci, Inst Software, Technol Ctr Software Engn, Beijing 100080, Peoples R China.