Analyzing conversations of Web services

A composite Web service consists of a set of individual services (or peers), which interact with each other via messages. A conversation is a global sequence of messages exchanged among peers participating in a composite Web service. Interestingly, conversation behavior differs significantly for synchronous and asynchronous communication, even if peers' local behaviors remain the same. The authors use synchronizability and realizability analysis techniques to analyze conversations in the presence of asynchronous communication. With these analyses, they can use model checking to automatically verify conversation behavior for bottom-up and top-down Web service specifications.     

语义Web服务——Web服务的扩展

语义Web服务是应用语义Web技术对Web服务的扩展.使信息具有语义就是用计算机内的Ontology中的概念作标记符对信息进行标记,对该过程予以支持的就是语义Web技术,即Ontology的构建技术、Ontology的使用技术(语义推理技术)和信息的语义标记技术.语义Web技术对Web服务的扩展可具体化为两项任务:服务提供者、服务请求者和服务注册处三类服务主体均内置Ontology;发布、查找和绑定三种交互信息均采用语义标记.     

RATEWeb: Reputation Assessment for Trust Establishment among Web services

We introduce RATEWeb, a framework for establishing trust in service-oriented environments. RATEWeb supports a cooperative model in which Web services share their experiences of the service providers with their peers through feedback ratings. The different ratings are aggregated to derive a service provider’s reputation. This in turn is used to evaluate trust. The overall goal of RATEWeb is to facilitate trust-based selection and composition of Web services. We propose a set of decentralized techniques that aim at accurately aggregating the submitted ratings for reputation assessment. We conduct experiments to assess the fairness and accuracy of the proposed techniques.     

Web services notifications

As Web services have matured, they've also acquired the need for asynchronous push capabilities. Early Web services, such as those for getting traffic or weather reports or for performing currency exchange-rate calculations, were seemingly all remote procedure calls-oriented. In an RPC system, the receiver typically performs the requested service and sends a response back to the caller over the same connection on which the request arrived, which means the details required by the service for sending a reply are implicit in the RPC network connection. Unfortunately, these kinds of implied communication details are wholly inadequate for asynchronous push Web services.     

Web services policies

In addition to the basic Web services architecture, various specifications already exist for adding security, reliable messaging, and transaction mechanisms to Web services messages. All of these include numerous options to let them meet various application requirements. Specifying option choices for Web services in basic communication areas such as security, reliable messaging, privacy, and transactions is the immediate goal underlying efforts to define Web services policies.     

Semantic Web services

The authors propose the markup of Web services in the DAML family of Semantic Web markup languages. This markup enables a wide variety of agent technologies for automated Web service discovery, execution, composition and interoperation. The authors present one such technology for automated Web service composition.     

Understanding Web services

Web services are a new breed of Web applications. These independent application components are published on to the Web in such a way that other Web applications can find and use them. They take the Web to its next stage of evolution, in which software components can discover other software components and conduct business transactions. Examples of Web services include a credit card service that processes credit card transactions for a given account number, a market data service that provides stock market data associated with a specified stock symbol, and an airline service that provides flight schedule, availability, and reservation functionalities. Major vendors like IBM, Microsoft, Hewlett-Packard, and Sun, among others, are investing heavily in Web services technology. Ranging from simple to complex, Web services bring the promise of flexible, open-standards-based, distributed computing to the Internet     

Putting the "Web" into Web services. Web services interaction models.2

For pt.1 see ibid., vol.6, no.3, p. 89-91 (2002). As I discussed in my previous column, each different style of middleware promotes one or more interaction models that determine how applications based on that middleware communicate and work with each other. It is difficult to say what the best interaction models would be for Web services, mainly because the World Wide Web Consortium (W3C) is still developing the architecture. The author considers the use of remote procedure calls, Web services and messaging and interface complexity.     

Discovering semantic associations among Web services based on the qualitative probabilistic network

In recent years, the intelligent management and decision of Web services have attracted more and more attention due to the wide applications in various aspects of the real world. With the increase of Web services in an organization, the desired on-line services should be located rapidly requiring not only the syntactic but also the semantic techniques. In addition, aiming at fulfilling complex applications by discovering and composing available services automatically and precisely, it is indispensable to develop an underlying model and the corresponding measure for semantic associations among given Web services. In this paper, by mining the historical invocations of component services, we first construct a semantic model to describe their behavior rules based on the qualitative probabilistic network. Further, we propose a distance measure and the approach to discovering semantic associations among Web services. Preliminary experiments and performance studies show that our methods are feasible. Moreover, high recall and precision can be achieved when our methods are applied to Web service search.     

Integration with Web services

There's a difference between what we'd like our enterprise computing systems to be and what they really are. We like to envision them as orderly multitier arrangements comprising software buses, hubs, gateways, and adapters - all deployed at just the right places to maximize scale, load, application utility, and ultimately, business value. Unfortunately, we know that there's a wide gulf between this idealistic vision and reality. In practice, our enterprise computing systems typically are tangles of numerous technologies, protocols, and applications, often hastily hard-wired together with inflexible point-to-point connections. The whole point of middleware is to hide the diversity and complexity of the computing machinery underneath it. By adopting the abstractions that middleware provides, we're supposedly isolating our applications from the variety of ever-changing hardware platforms, operating systems, networks, protocols, and transports that make up our enterprise computing systems. We can use Web services to provide "middleware for middleware" abstraction layer for modern integration applications.     

Constructing dependable Web services

The majority of today's millions of Web sites offer read-only access to relatively small amounts of infrequently changing information. The load on these sites is usually small, and services can often be hosted as background tasks on general-purpose workstations. Concern for the quality of service (QoS) presented to users at these sites is generally not primary. Conversely, a much smaller number of sites are very popular; they support heavy loads and must meet user expectations regarding QoS to maintain their popularity. We discuss issues involved in supporting high-volume, high-reliability Web services. We begin by surveying the diverse technical challenges and constraints posed in this environment, followed by currently used hardware and network based approaches to meeting the scalability requirements and software-implemented techniques to addressing fault tolerance. However, these approaches do not scale well, so we discuss possible alternatives     

Web services choreography validation

In this paper, we propose an approach to simulation and validation of Web services choreography described by WS-CDL. Simulation of Web services choreography is important to analyze and test the choreography model written by SOA designers. On the other hand, WS-CDL specification regulates the correct behaviors a WS-CDL document has to obey. Thus, constraints are specified in WS-CDL specification including static, dynamic and implementation ones. We developed a relational calculus to capture those constraints precisely, and a corresponding algorithm for relational analysis is performed with the WS-CDL parser and simulator. Last but not least, a tool called CDLchecker is developed to facilitate designers to simulate and validate WS-CDL documents.     

Agents as Web services

Web services are extremely flexible. Most advantageously, a developer of Web services need not know who or what will use the services being provided. The paper discusses current standards for Web services, directory services and the Semantic Web. It considers how agents extend Web services in several important ways.     

Autonomous Semantic Web services

The Web is a collection of human-readable pages that are virtually unintelligible to computer programs. While the Web emerged as a global repository of digitized information, this very information is, by and large, unavailable for automatic computation. Two parallel efforts have emerged in recent years that could overcome this paradox: the Semantic Web is providing tools for explicit markup of Web content, and Web services could create a network in which programs act as independent agents that produce and consume information, enabling automated business transactions. The DARPA Agent Markup Language for Services (DAML-S) provides a mechanism that begins to bridge the gap between the Web services infrastructure and the Semantic Web.     

Web services interoperability specifications

A proposed conceptual framework for analyzing Web services interoperability issues provides a context for studying existing standards and specifications and for identifying new opportunities to provide automated support, for this technology. Web services are becoming the technology of choice for realizing service-oriented architectures (SOAs). Web services simplify interoperability and, therefore, application integration. They provide a means for wrapping existing applications so developers can access them through standard languages and protocols.     

基于Axis开发Web服务的研究

Web Services已成为网络应用发展的主流,SOAP协议是Web Services的核心协议。Axis本身是基于Java语言开发的项目,它给出了一个很好的SOAP实现平台,基于它开发Web Services应用省掉了许多底层技术细节,从而使Web服务的开发变得轻松高效。结合图示和应用例子,主要介绍了Axis的工作原理、主要的相关技术WSDL,以及使用Axis时的环境设置、开发和部署Web服务的不同方法。