A formal model for the interoperability of service clouds

Large-scale service-oriented computing is based on the idea that services from various servers are combined into one distributed application. Referring to a collection of services on one server as a ??service cloud??, the problem investigated in this paper is to define formal high-level specifications of such distributed applications and to enable the location of suitable services for them. Based on the language-independent model of Abstract State Services (AS²s), which serves as a universal integrated model for data and software as services, we extend AS²s by high-level action schemes called ??plots?? as a means to specify permitted sequences of service operations. On these grounds, we develop a model for service mediators, that is, specifications of composed services in which service slots have to be filled by actual services, and investigate matching conditions for slots of mediators and services. For a services to match a slot in a mediator, a (generalised) projection of the mediator must comply with the plot of the service. Furthermore, the service must be semantically adequate, which requires the use of a service ontology.     

Explanation-aware service selection: rationale and reputation

A collection of 1 billion¹ publicly available web services can form an internet-scale infrastructure for building diverse applications. For a given application, selection of services and service providers from this collection becomes important and reputation is recognized as a key factor for this purpose. However, current reputation systems are limited in their ability to exchange reputation information between heterogeneous systems. To facilitate meaningful exchange and reuse of reputation information and for the overall determination of reputation, we identify the need to infer and explicate rationale for ratings. We present our knowledge-based approach to inferring and explicating rationale for ratings. We show that this approach facilitates detection of deception and collusion, user preference elicitation, explication of rationale behind user ratings and generation of personalized service recommendations.     

Standards for image annotation using Semantic Web

The impetus behind Semantic Web research remains the vision of supplementing availability with utility; that is, the World Wide Web provides availability of digital media, but the Semantic Web will allow presently available digital media to be used in unseen ways. An example of such an application is multimedia retrieval. At present, there are vast amounts of digital media available on the web. Once this media gets associated with machine-understandable metadata, the web can serve as a potentially unlimited supplier for multimedia web services, which could populate themselves by searching for keywords and subsequently retrieving images or articles, which is precisely the type of system that is proposed in this paper. Such a system requires solid interoperability, a central ontology, semantic agent search capabilities, and standards. Specifically, this paper explores this cross-section of image annotation and Semantic Web services, models the web service components that constitute such a system, discusses the sequential, cooperative execution of these Semantic Web services, and introduces intelligent storage of image semantics as part of a semantic link space.     

基于抽象解释的服务间消息的数据约减

面向服务软件中服务间消息的变量值可能存在无穷域的情况,从而导致模型检测时产生状态空间爆炸问题。为了使终止性验证在实践上可行,需要约减模型状态空间的大小,使得计算时间和空间需求合理。为此,基于抽象解释的区间抽象理论扩展了经典区间抽象域方法,并在统一的区间抽象域方法上借助异常控制流图对变量进行区间分析,在此基础上逆向分析得到服务间消息的变量区间集。变量区间上任意值相对于终止性验证是等价性,因此从每一个变量区间集中选取一个代表值,可组成服务间消息变量的约减值,从而为异常处理的终止性验证提供了约减的初始配置,有效避免了状态空间爆炸。     

A formal and visual modeling approach to choreography based web services composition and conformance verification

Web services have emerged as the building blocks of a service-oriented architecture that supports not only enterprise application integration (EAI) and business process management (BPM) within an organization but also B2B collaboration based on business process integration. The web services choreography approach to B2B process integration allows business partners to orchestrate their own web services privately, while conforming with an agreed specification of the common ordering conditions and constraints under which messages are exchanged among partners’ web services. In this approach, choreography conformance is an essential requirement for the successful implementation of collaborative processes. A formal approach to web services composition and conformance verification based on WS-CDL and WS-BPEL is presented. This approach involves model checking as an automated means of verifying choreography conformance. The main contributions include a precise notion of choreography conformance on which verification is based as well as support for the complementary use of visual modeling (e.g. UML) and standard WS-¹ notations in composition.     

Supporting the semi-automatic semantic annotation of web services: A systematic literature review

ContextSemantically annotating web services is gaining more attention as an important aspect to support the automatic matchmaking and composition of web services. Therefore, the support of well-known and agreed ontologies and tools for the semantical annotation of web services is becoming a key concern to help the diffusion of semantic web services.ObjectiveThe objective of this systematic literature review is to summarize the current state-of-the-art for supporting the semantical annotation of web services by providing answers to a set of research questions.MethodThe review follows a predefined procedure that involves automatically searching well-known digital libraries. As a result, a total of 35 primary studies were identified as relevant. A manual search led to the identification of 9 additional primary studies that were not reported during the automatic search of the digital libraries. Required information was extracted from these 44 studies against the selected research questions and finally reported.ResultsOur systematic literature review identified some approaches available for semantically annotating functional and non-functional aspects of web services. However, many of the approaches are either not validated or the validation done lacks credibility.ConclusionWe believe that a substantial amount of work remains to be done to improve the current state of research in the area of supporting semantic web services.     

Modeling and generating realistic streaming media server workloads

Currently, Internet hosting centers and content distribution networks leverage statistical multiplexing to meet the performance requirements of a number of competing hosted network services. Developing efficient resource allocation mechanisms for such services requires an understanding of both the short-term and long-term behavior of client access patterns to these competing services. At the same time, streaming media services are becoming increasingly popular, presenting new challenges for designers of shared hosting services. These new challenges result from fundamentally new characteristics of streaming media relative to traditional web objects, principally different client access patterns and significantly larger computational and bandwidth overhead associated with a streaming request. To understand the characteristics of these new workloads we use two long-term traces of streaming media services to develop MediSyn, a publicly available streaming media workload generator. In summary, this paper makes the following contributions: (i) we propose a framework for modeling long-term behavior of network services by capturing the process of file introduction, non-stationary popularity of media accesses, file duration, encoding bit rate, and session duration. (ii) We propose a variety of practical models based on the study of the two workloads. (iii) We develop an open-source synthetic streaming service workload generator to demonstrate the capability of our framework to capture the models.     

Composing web services enacted by autonomous agents through agent-centric contract net protocol

ContextAgents are considered as one of the fundamental technologies underlying open and dynamic systems that are largely enabled by the semantic web and web services. Recently, there is a trend to introduce the notion of autonomy empowered by agents into web services. However, it has been argued that the characteristics of autonomy will make agents become available intermittently and behave variedly over time, which therefore increase the complexity on devising mechanisms for composing services enacted by autonomous agents.ObjectiveIn this work, we propose an extension to Contract Net protocol, called Agent-centric Contract Net Protocol (ACNP), as a negotiation mechanism with three key features for composing web services enacted by autonomous agents.Method(1) A matchmaking mechanism embedded in a middle agent (as a service matchmaker) for discovering web services that are available intermittently is presented based on the concept of agent roles; (2) A selection algorithm based on risk-enabled reputation model (REAL) embedded in a manager agent (as a service composer) is introduced to serve a basis for selecting web services with variant performance; and (3) A negotiation mechanism between a manager agent and contractor agents (as atomic services) is devised and enables both a service composer and the atomic services to request, refuse or agree on adapting changes of services.ResultsThe problem of assembling a computer is discussed in this paper.ConclusionIt is increasingly recognised that web services would become more autonomous by introducing diverse agent technologies to better constitute more complex systems in open and dynamic environments. As web service technologies are best exploited by composite services, it is imperative to devise mechanisms for composing services of autonomy.     

Computing performance requirements for web service compositions

In order to produce service compositions, modern web applications now combine both in-house and third-party web services. Therefore, their performance depends on the performance of the services that they integrate. At early stages, it may be hard to quantify the performance demanded from the services to meet the requirements of the application, as some services may not be available or may not provide performance guarantees. The authors present several algorithms that compute the required performance for each service from a model of a service composition at an early stage of development. This is also helpful when testing service compositions and selecting candidate web services, enabling performance-driven recommendation systems for web services that could be integrated into service discovery. Domain experts can annotate the model to include partial knowledge on the expected performance of the services. We develop a throughput computation algorithm and two time limit computation algorithms operating on such a model: a baseline algorithm, based on linear programming, and an optimised graph-based algorithm. We conduct theoretical and empirical evaluations of their performance and capabilities on a large sample of models of several classes. Results show that the algorithms can provide an estimation of the performance required by each service, and that the throughput computation algorithm and the graph-based time limit computation algorithm show good performance even in models with many paths.     

A WSDL-based type system for asynchronous WS-BPEL processes

We tackle the problem of providing rigorous formal foundations to current software engineering technologies for web services, and especially to WSDL and WS-BPEL, two of the most used XML-based standard languages for web services. We focus on a simplified fragment of WS-BPEL sufficiently expressive to model asynchronous interactions among web services in a network context. We present this language as a process calculus-like formalism, that we call ws-calculus, for which we define an operational semantics and a type system. The semantics provides a precise operational model of programs, while the type system forces a clean programming discipline for integrating collaborating services. We prove that the operational semantics of ws-calculus and the type system are ‘sound’ and apply our approach to some illustrative examples. We expect that our formal development can be used to make the relationship between WS-BPEL programs and the associated WSDL documents precise and to support verification of their conformance.     

A new cloud computing architecture for music composition

This paper presents an original cloud computing architecture for music composition. In this model, music applications are built by making several computer music services work together. Component services are provided by a dedicated layer in the cloud architecture called computer music as a Service (CMaaS). The specialized music services can be integrated into different applications at the same time. These music services provided by the CMaaS layer are implemented in the form of platform images based on templates at the Platform as a Service layer. The images are ready to be loaded into the virtualized infrastructure on demand. As examples of implementation over the proposed cloud architecture, two powerful applications for computer music composition are presented: “Diatonic Composer”, an interactive composer of scores with high-abstraction music elements, and “Csound Meets the Cloud”, an assisted algorithmic composer focused on sound synthesis. The composition model, the involved music services and the web application are described for the above mentioned applications. The proposed architecture, the implemented services and the provided application examples constitute a decided step towards distributed music computation.     

Time-constrained services: a framework for using real-time web services in industrial automation

The use of web services in industrial automation, e.g. in fully automated production processes like car manufacturing, promises simplified interaction among the manufacturing devices due to standardized protocols and increased flexibility with respect to process implementation and reengineering. Moreover, the adoption of web services as a seamless communication backbone within the overall industrial enterprise has additional benefits, such as simplified interaction with suppliers and customers (i.e. horizontal integration) and avoidance of a break in the communication paradigm within the enterprise (i.e. vertical integration). The Time-Constrained Services (TiCS) framework is a development and execution environment that empowers automation engineers to develop, deploy, publish, compose, and invoke time-constrained web services. TiCS consists of four functional layers—tool support layer, real-time infrastructural layer, real-time service layer, and hardware layer—which contain several components to meet the demands of a web service based automation infrastructure. This article gives an overview of the TiCS framework. More precisely, the general design considerations and an architectural blueprint of the TiCS framework are presented. Subsequently, selected key components of the TiCS framework are discussed in detail: the SOAP4PLC engine for equipping programmable logic controllers with a web service interface, the SOAP4IPC engine for processing web services in real-time on industrial PCs, the WS-TemporalPolicy language for describing time constraints, and the TiCS Modeler for composing time-constrained web services into a time-constrained BPEL4WS workflow.     

面向浏览器的医学影像可视化系统

目的 当前各大商业公司和开源社区所提供的医学影像可视化系统依赖于各类平台以及与平台相关的插件,难以实现跨平台访问.为此提出并实现了基于HTML5的面向现代浏览器的医学影像可视化系统.方法 基于B/S(browers/server)模式进行系统整体架构与设计,设计自定义的传输协议提供各种定制的图像可视化服务.对于2维影像,采用HTML的canvas技术和WebGL技术进行浏览器端硬件加速.对于3维医学影像,采用前后端异步操作的策略以提供渐进式可视化.算法构造原始数据的多分辨率采样,并在用户交互过程中实现自适应可视化.结果 在不同的浏览器、多组临床医学影像肝脏数据上测试了系统,表明系统支持跨浏览器的可视化.测试2维和3维可视化的结果表明,系统支持2维影像的实时可视化(25帧/s),支持3维影像的交互可视化.对于512×512×154的医学体数据,低精度绘制模式的可视化效率可以达到60帧/s,高精度绘制模式的可视化效率可达到 1帧/s 的绘制效率.结论 本文面向浏览器的医学影像可视化系统利用当下新兴的WEB技术实现了跨浏览器、跨平台地对用户提供服务,为远程及移动医疗影像可视化系统提供了机会.     

On the use of parallel processors for implicit Runge-Kutta methods

An iteration scheme, for solving the non-linear equations arising in the implementation of implicit Runge-Kutta methods, is proposed. This scheme is particularly suitable for parallel computation and can be applied to any method which has a coefficient matrixA with all eigenvalues real (and positive). For such methods, the efficiency of a modified Newton scheme may often be improved by the use of a similarity transformation ofA but, even when this is the case, the proposed scheme can have advantages for parallel computation. Numerical results illustrate this. The new scheme converges in a finite number of iterations when applied to linear systems of differential equations, achieving this by using the nilpotency of a strictly lower triangular matrixS ^?1 AS — Λ, with Λ a diagonal matrix. The scheme reduces to the modified Newton scheme whenS ^?1 AS is diagonal.A convergence result is obtained which is applicable to nonlinear stiff systems.     

SipaaS: Spot instance pricing as a Service framework and its implementation in OpenStack

Designing dynamic pricing mechanisms that efficiently price resources in line with a provider's profit maximization goal is a key challenge in cloud computing environments. Despite the large volume of research published on this topic, there is no publicly available software system implementing dynamic pricing for Infrastructure as a Service cloud spot markets. This paper presents the implementation of a framework called Spot instance pricing as a Service (SipaaS) that supports an auction mechanism to price and allocate virtual machine instances. SipaaS is an open‐source project offering a set of web services to price and sell virtual machine instances in a spot market resembling the Amazon EC2 spot instances. Cloud providers, who aim at utilizing SipaaS, should install add‐ons in their existing platform to make use of the framework. As an instance, we provide an extension to the Horizon – the OpenStack dashboard project – to employ SipaaS web services and to add a spot market environment to OpenStack. To validate and evaluate the system, we conducted an experimental study with a group of 10 users utilizing the provided spot market in a real environment. Results show that the system performs reliably in a practical test environment. Copyright © 2015 John Wiley & Sons, Ltd.     

Incremental and interactive mining of web traversal patterns

Web mining involves the application of data mining techniques to large amounts of web-related data in order to improve web services. Web traversal pattern mining involves discovering users’ access patterns from web server access logs. This information can provide navigation suggestions for web users indicating appropriate actions that can be taken. However, web logs keep growing continuously, and some web logs may become out of date over time. The users’ behaviors may change as web logs are updated, or when the web site structure is changed. Additionally, it can be difficult to determine a perfect minimum support threshold during the data mining process to find interesting rules. Accordingly, we must constantly adjust the minimum support threshold until satisfactory data mining results can be found.The essence of incremental data mining and interactive data mining is the ability to use previous mining results in order to reduce unnecessary processes when web logs or web site structures are updated, or when the minimum support is changed. In this paper, we propose efficient incremental and interactive data mining algorithms to discover web traversal patterns that match users’ requirements. The experimental results show that our algorithms are more efficient than other comparable approaches.     

A theoretical investigation of the emerging standards for web services

Currently, standards for web services are being developed via three different initiatives (W3C, Semantic web services and ebXML). To the best of our knowledge, no theoretical perspectives underlie these standardization efforts. Without the benefit of a strong theoretical basis, the results, within and across these initiatives, have remained piecemeal. We suggest ‘Language–Action Theories’ as a plausible perspective that can effectively define, assess and refine web services standards. In this paper, we first investigate the existing initiatives to identify commonalities that point to theories of ‘Language–Action’ as an appropriate theoretical basis for web services standards. Next, we adapt work from these theories to develop a comprehensive reference framework for understanding web services standards. Finally, we use this reference framework to assess the three initiatives, and analyze the findings to provide insights for future development and refinement of web services standards.