Models as web services using the Open Geospatial Consortium (OGC) Web Processing Service (WPS) standard

Environmental modeling often requires the use of multiple data sources, models, and analysis routines coupled into a workflow to answer a research question. Coupling these computational resources can be accomplished using various tools, each requiring the developer to follow a specific protocol to ensure that components are linkable. Despite these coupling tools, it is not always straight forward to create a modeling workflow due to platform dependencies, computer architecture requirements, and programming language incompatibilities. A service-oriented approach that enables individual models to operate and interact with others using web services is one method for overcoming these challenges. This work advances the idea of service-oriented modeling by presenting a design for a modeling service that builds from the Open Geospatial Consortium (OGC) Web Processing Service (WPS) protocol. We demonstrate how the WPS protocol can be used to create modeling services, and then demonstrate how these modeling services can be brought into workflow environments using generic client-side code. We implemented this approach within the HydroModeler environment, a model coupling tool built on the Open Modeling Interface standard (version 1.4), and show how a hydrology model can be hosted as a WPS web service and used within a client-side workflow. The primary advantage of this approach is that the server-side software follows an established standard that can be leveraged and reused within multiple workflow environments and decision support systems.     

空间信息网格中异步Web计算服务设计与实现

目前空间信息网格平台上的计算处理功能通常是以Web服务形式对外发布的,而较长时间的处理任务通常会导致Web服务超时,同时现有的处理服务大都基于各自制定的私有协议,相互之间难以实现互操作。本文针对上述问题,在充分分析OGC的Web处理服务基础上,给出了一种基于OGC标准的异步Web处理服务框架。基于该框架实现的处理算法,可以避免因为计算时间过长而失去响应的问题,同时该框架也具有很好的扩展性,算法提供者可以很容易的将自己的算法集成到已有的服务中。同时该服务框架遵循WPS标准,可以与其他遵循WPS标准的处理服务实现互操作与资源共享。     

面向OWS地理信息服务的描述词汇约简模型研究

地理信息服务在发展进程中缺乏对服务信息的语义描述,处于数据丰富而知识缺乏的境地,要充分利用大量的已有数据信息,则必须对数据做一些精化处理,就迫切需要一种从大数据量中发现、提取知识的有效方法。该研究以OGC网络服务（OGC Web Service,OWS）为研究对象,基于OWS服务的XML文档和描述词汇,对搜集到的OWS服务进行解析,并引入粗糙集理论的约简方法,建立面向OWS服务的描述词汇约简模型,从而对解析后的OWS服务进行约简,最终形成OWS服务最优描述词汇集,为后续OWS语义推理奠定基础。     

A high performance backoff protocol for fast execution of composite web services

Using web services to expose applications over the Internet is now a widely accepted practice. Currently, there are several ongoing efforts that provide ways to effectively compose web services distributed across different organizations. One of the problems underlying the deployment of such composite services on the web, however, is service co-allocation that arises when a composite service needs to ensure all the required component services to be available for execution at the same time. Motivated by this, this paper presents a new decentralized protocol, named web service co-allocation protocol (WSCP), which can facilitate fast execution of composite web services. The proposed framework is an enhancement of the famous two phase commit protocol through the incorporation of tentative hold phase as well as the employment of a new high performance backoff protocol developed to better address the dynamics of the service co-allocation problem. The simulation results show that the proposed approach yields significant improvements over existing protocols.     

Development of the Arctic Research Mapping Application (ARMAP): Interoperability challenges and solutions

Ensuring interoperability between WebGIS applications is essential for maximizing access to data, data sharing, and data manipulation. Interoperability is maximized through the adoption of best practices, use of open standards, and utilization of spatial data infrastructure (SDI). While many of the interoperability challenges like infrastructure, data exchange, and file formats are common between applications, some regions like the Arctic present specific challenges including the need for presenting data in one or more polar projections. This paper describes the Arctic Research Mapping Application (ARMAP) suite of online interactive maps, web services, and virtual globes (the ARMAP suite; http://armap.org/) and several of the interoperability challenges and solutions encountered in development to date. ARMAP is a unique science and logistic tool supporting United States and international Arctic science by providing users with the ability to access, query, and browse information and data. Access to data services include a text-based search utility, an Internet Map Server client (ArcIMS), a lightweight Flex client, ArcGIS Explorer and Google Earth virtual globes, and Open Geospatial Consortium (OGC) compliant web services, such as Web Map Service (WMS) and Web Feature Service (WFS). Through the ARMAP suite, users can view a variety of Arctic map layers and explore pertinent information about United States Arctic research efforts. The Arctic Research Logistics Support Service (ARLSS) database is the informational underpinning of ARMAP. Avoiding duplication of effort has been a key priority in the development of the ARMAP applications. The ARMAP suite incorporates best practices that facilitate interoperability such as Federal Geographic Data Committee (FGDC) metadata standards, web services for embedding external data and serving framework layers, and open standards such as Open Geospatial Consortium (OGC) compliant web services. Many of the features and capabilities of ARMAP are expected to greatly enhance the development of an Arctic SDI.     

一种面向网构软件体系结构的信任驱动服务选取机制

基于信任度评估的思想,从软件服务选取的角度对此问题进行了探讨,提出一种面向网构软件体系结构的信任驱动的服务选取机制:首先,给出一种通用的、机器可理解的应用需求及信任演化策略描述规范;其次,采用一种基于反馈的信任形成及决策机制,并给出一个信任驱动的服务选取算法;最后,给出一种面向网构软件体系结构的信任驱动的服务选取支撑框架.初步实践表明,上述机制为开发可信网构软件提供了有效支持.     

RESTful风格地图瓦片服务的研究

综合当前主流的WebGIS产品和瓦片缓存技术,对地图瓦片服务的重要性和未来WebGIS产品应用的趋势进行了分析.详细阐述了OGC地图瓦片服务执行规范1.0.0版本的重点内容;并且介绍了RESTful风格服务的设计原则.充分利用现有的Web基础设施,从实现的角度给出了地图瓦片服务的体系架构,整体流程,按目录存储地图瓦片的具体结构,以及地图库访问引擎模块的功能接口的实现,完成基于RESTful风格的OGC地图瓦片服务的实现.     

一种面向服务的软件Agent设计模型

软件Agent的设计实现对于解决网络分布环境中的很多应用问题都非常重要。本文在基于事件处理的概念级软件Agent设计模型的基础上,针对Web服务的特殊要求,做出了相应的模型改进。首先对三个知识库进行了细化,然后给出了面向服务的软件Agent内部决策算法过程;考虑到Web服务对Agent协同的要求,还提供了软件Agent必须遵守的交互参考协议。     

基于有限状态自动机的组合Web服务性能优化

组合Web服务的业务流程可以通过有限状态自动机来描述。传统的组合Web服务采用集中式的执行方式,它会带来不必要的网络流量和数据堵塞,造成大量的通信开销。提出一种基于有限状态自动机的非集中式的执行策略,在自动机的状态空间中运用启发式搜索算法执行总体代价最优的路径,从而有效减少消息传递数量,提高系统吞吐量。基于该方案设计了一个原型系统来验证系统整体性能的最优化。     

基于SAML和XACML的Web服务访问控制模型

Web服务采用了通用的协议和技术,便于用户访问,已成为了分布式计算的研究热点,但这种方便也带来了安全性的隐患。提出了一个基于SAML和XACML的Web服务访问控制模型,利用SAML协议实现单点登录,采用XACML策略描述语言对用户进行访问控制。模型在扩展SAML协议的基础上,把XACML引入Web服务能够更好地对服务端受保护资源进行控制,从而实现Web服务的安全访问控制。     

Web Service Diagnoser Model for managing faults in web services

Reliability is an important criterion to facilitate extensive deployment of web service technology for commercial business applications. Run-time monitoring and fault management of web services are essential to ensure uninterrupted and continuous availability of web services. This paper presents WISDOM (Web Service Diagnoser Model) a generic architecture for detecting faults during execution of web services. Policies have been proposed to describe the intended behavior of web services and faulty behavior would be detected as deviations or inconsistencies with respect to the specified behavior. The model proposes the use of monitoring components in service registries and service providers to detect run-time faults during publishing, discovery, binding and execution of web services. An independent fault diagnoser is proposed to coordinate the individual monitoring components and also act as a repository for the specified web service policies. The proposed model has been tested with a sample web service application and the results obtained are presented.     

Minimal privacy authorization in web services collaboration

With the popularity of Internet technology, web services are becoming the most promising paradigm for distributed computing. This increased use of web services has meant that more and more personal information of consumers is being shared with web service providers, leading to the need to guarantee that the private data of consumers are not illegitimate collected, used and disclosed in services collaboration. This paper studies how to realize the minimal privacy authorization while achieving the functional goals. Initially, this paper uses authorization policies to specify the privacy privileges of the services collaboration, and utilizes the trust relationships among services to make authorization decision. Next, it models the interface behaviors of services by extending the interface automata to support privacy semantics. Furthermore, it quantitatively analyzes the minimum set of privacy privileges which are required by the services to achieve the functional goals, and presents the minimal authorization algorithm, which helps us to automatically derive optimal authorization policies for a services collaboration. Finally, it verifies the correctness and efficiency of the approach proposed by this paper through a case study.     

A meta-control architecture for orchestrating policy enforcement across heterogeneous information sources

There is increasing demand from both organizations and individuals for technology capable of enforcing sophisticated, context-sensitive policies, whether security and privacy policies, corporate policies or policies reflecting various regulatory requirements. In open environments, enforcing such policies requires the ability to reason about the policies themselves as well as the ability to dynamically identify and access heterogeneous sources of information. This article introduces a semantic web framework and a meta-control model to orchestrate policy reasoning with the identification and access of relevant sources of information. Specifically, sources of information are modeled as web services with rich semantic profiles. Policy Enforcing Agents rely on meta-control strategies to dynamically interleave semantic web reasoning and service discovery and access. Meta-control rules can be customized to best capture the requirements associated with different domains and different sets of policies. This architecture has been validated in the context of different environments, including a collaborative enterprise domain as well as several mobile and pervasive computing applications deployed on Carnegie Mellon's campus. We show that, in the particular instance of access control policies, the proposed framework can be viewed as an extension of the XACML architecture, in which Policy Enforcing Agents offer a particularly powerful way of implementing XACML's Policy Information Point (PIP) and Context Handler functionality. At the same time, our proposed architecture extends to a much wider range of policies and regulations. Empirical results suggest that the semantic framework introduced in this article scales favorably on problems with up to hundreds of services and tens of service directories.     

A tentative commit protocol for composite web services

Composite web services provide promising prospects for conducting cross-organizational business transactions. Such transactions: are generally complex, require longer processing time, and manipulate financially critical data. It is therefore crucial to ensure stronger reliability, higher throughput and enhanced performance of transactions. In order to meet these requirements, this paper proposes a new commit protocol for managing transactions in composite web services. Specifically, it aims to improve the performance by reducing network delays and the processing time of transactions. The proposed protocol is based on the concept of tentative commit that allows transactions to tentatively commit on the shared data of web services. The tentative commit protocol avoids resource blocking thus improving performance. The proposed protocol is tested through various simulation experiments. The outcomes of these experiments show that the proposed protocol outperforms existing protocols in terms of transaction performance.     

Secure web services using two-way authentication and three-party key establishment for service delivery

With the advance of web technologies, a large quantity of transactions have been processed through web services. Service Provider needs encryption via public communication channel in order that web services can be delivered to Service Requester. Such encryptions can be realized using secure session keys. Traditional approaches which can enable such transactions are based on peer-to-peer architecture or hierarchical group architecture. The former method resides on two-party communications while the latter resides on hierarchical group communications. In this paper, we will use three-party key establishment to enable secure communications for Service Requester and Service Provider. The proposed protocol supports Service Requester, Service Broker, and Service Provider with a shared secret key established among them. Compared with peer-to-peer architecture and hierarchical group architecture, our method aims at reducing communication and computation overheads.     

Web Services中的消息通信研究

首先介绍了Web Services的体系结构与基本可交互协议栈,然后介绍了消息通信的基础,提出在Web Services中通过消息通信机制能很好地解决传统RPC技术存在的性能、可靠性和多点支持的问题,接着详细描述了Web Services中进行消息通信的两个关键组成部分：缓冲和回调;最后通过示例讲述了创建Web Services消息通信的过程。     

一个基于WSIF的Web服务调用方法

针对传统的Web服务调用机制无法适应SOAP服务器多样性的问题,研究WSIF的工作原理,设计一个通用的独立于SOAP协议的Web服务调用方法.该方法能够隐藏Web服务底层访问协议的复杂性,使用户可以直接从WSDL文档中自动提取Web服务的方法和参数,在SOAP服务器端发生改变的情况下,可无需改动客户端程序就能快速实现远程Web服务的动态异步调用.研究表明,该方法该可以适应SOAP服务器多样性,提高Web服务访问效率.