The role of models@run.time in supporting on-the-fly interoperability

Models at runtime can be defined as abstract representations of a system, including its structure and behaviour, which exist in tandem with the given system during the actual execution time of that system. Furthermore, these models should be causally connected to the system being modelled, offering a reflective capability. Significant advances have been made in recent years in applying this concept, most notably in adaptive systems. In this paper we argue that a similar approach can also be used to support the dynamic generation of software artefacts at execution time. An important area where this is relevant is the generation of software mediators to tackle the crucial problem of interoperability in distributed systems. We refer to this approach as emergent middleware, representing a fundamentally new approach to resolving interoperability problems in the complex distributed systems of today. In this context, the runtime models are used to capture meta-information about the underlying networked systems that need to interoperate, including their interfaces and additional knowledge about their associated behaviour. This is supplemented by ontological information to enable semantic reasoning. This paper focuses on this novel use of models at runtime, examining in detail the nature of such runtime models coupled with consideration of the supportive algorithms and tools that extract this knowledge and use it to synthesise the appropriate emergent middleware.     

一种中间件服务容错配置管理方法

提出一种基于运行时刻软件体系结构的容错管理方法,支持开发者和管理员针对不同中间件服务失效定制合适的故障检测和修复机制.首先,运行时刻软件体系结构自动构造构件依赖视图和错误传播①视图,为理解和分析整个系统的可靠性提供全局视图;然后,操作运行时刻软件体系结构配置容错机制;最后利用AOP技术将容错机制插装到中间件中,使其具备指定的容错能力.上述过程在一个可视化工具的辅助下半自动实施,并在J2EE中间件上得到验证.     

IP电话业务系统与多层分布式体系技术

随着IP增值业务的不断发展以及Internet的发展普及,新的分布式应用系统产生了,它将业务处理与客户交互分开来,实现了瘦客户/业务服务/数据服务的多层分布式体系结构。文中对以中间件为基础框架的多层分布式体系技术进行了介绍,分析了多层分布式体系技术在电信IP电话业务中的应用,给出了相关体系流程和MQ消息中间件的多层分布式体系事例。     

软件体系结构驱动的运行环境

由于软件体系结构以隐性的方式存在，结构的问题被传播到平台内，运行时软件体系结构不能在应用层次上被观察和控制，系统难以联机动态演化．在现有的中间件平台之上设计了一个面向应用、开放的、软件体系结构驱动的分布式远行环境SADRE（Software Architecture—Driven Runtime Environment），软件体系结构在可运行系统中以一类实体显性地表示,体系结构描述作为核心元素被整个分布式运行环境共事，成为系统调度、通信的依据．从而驱动用户应用的运行．SADRE为灵活的动态体系结构提供了良好的支持，提高了系统的柔性和扩展性．     

中间件技术在电信自助服务平台中的应用

介绍了电信自助服务平台的系统构成,着重讨论了中间件技术在开发电信自助服务平台上的实现方法,并提供了用中间件实现分布式事务处理系统的关键技术。利用该技术设计的“自助服务管理系统”已在中国联通湖南分公司得到成功应用。     

基于反模式的中间件应用系统性能优化

提出了一种基于反模式的中间件应用系统的性能优化方法.该方法的主要特点包括:建立了反模式元模型以使得反模式的表示更加准确:综合利用系统的静态信息和动态信息以检测运行系统中存在的反模式;系统重构在不中断应用系统运行的前提下在线执行,并在中间件的辅助下自动/半自动地完成.在J2EE平台上实现了支持该方法的原型系统,并通过网上书店的实例展示了该方法的有效性.     

企业级Java Web服务的研究与实现

企业级Java Web 服务是一种基于Java 技术实现的企业级分布式组件技术, 解决了Web 服务访问过程中的状态保持问题, 基于HTTP 和JMS 协议支持对Web 服务的多种调用方式, 采用灵活的配置获得多种中间件服务的支持, 并利用Web 服务的包容性实现了对多种异构遗留系统的集成, 从而为将Web 服务应用到企业级的环境中提供了足够的保障。利用一个企业级Java Web 服务组件模型, 并基于此实现了一个运行时系统, 系统由客户端、消息中间件和运行时容器三部分组成, 支持业务客户端与服务端企业级     

Non-functional Oriented Dynamic Integration Of Distributed Components

Building distributed systems from scratch is known as one of the most difficult and time consuming process in software engineering. A great deal of progress has been made in the development of middleware and techniques to facilitate the process of distributed systems through integrating reusable components and customizing middleware. However, most of these solutions tend to focus on the functional aspects of the components and how to adapt their behavior according to their needs. Although the non-functional properties of the services are equally important, because of the difficulties in representing and controlling them, they are usually neglected. This paper investigates the problem of distributed systems' non-functional properties and describes a framework that presents a solution to the problem. The framework is based on the idea of defining the non-functional properties of the services at the early stages of the design and incorporating such properties within the architecture to ease the process of managing the system at run time.     

A cross-layer optimized storage system for workflow applications

This paper proposes using file system custom metadata as a bidirectional communication channel between applications and the storage middleware. This channel can be used to pass hints that enable cross-layer optimizations, an option hindered today by the ossified file-system interface. We study this approach in the context of storage system support for large-scale workflow execution systems: Our workflow-optimized storage system (WOSS), exploits application hints to provide per-file optimized operations, and exposes data location to enable location-aware scheduling. We argue that an incremental adoption path for adopting cross-layer optimizations in storage exists, present the system architecture for a workflow-optimized storage system and its integration with a workflow runtime engine, and evaluate this approach using synthetic and real applications over multiple success metrics (application runtime, generated network stress, and energy). Our performance evaluation demonstrates that this design brings sizeable performance gains. On a large scale cluster (100 nodes), compared to two production class distributed storage systems (Ceph and GlusterFS), WOSS achieves up to 6× better performance for the synthetic benchmarks and 20–40% better application-level performance gain for real applications.     

Web应用服务器的适应性失效检测

失效检测是分布式系统的基本可靠性保障技术,它对运行时系统的存活状态进行及时检测.作为网络分布计算环境中的主流中间件,Web应用服务器(Web application server,简称WAS)需要提供良好的检测机制,并且要能满足适应性的需求.适应性失效检测要求失效检测器能够根据应用需求和系统环境的变化而动态地改变检测的质量.首先给出了WAS的多层失效检测模型,然后基于失效检测器的服务质量规约,提出了适应性失效检测算法,并设计了一个WAS的适应性失效检测框架.它能够满足动态调整失效检测质量和灵活集成失效检测器的要求.该工作在OnceAS应用服务器中进行了实现,并给出了OnceAS平台上的实验及数据.     

基于JSP与Notes架构B/S的电信管理信息系统

电信业务系统难以集成、数据共享困难是目前电信企业信息化建设面临的主要问题 ,本文介绍了如何架构基于B/S模式的融办公、管理和决策为一体的电信企业管理信息系统。还介绍了采用JSP技术实现MIS的主体部分 ,并结合Notes的Web开发技术实现基于浏览器的办公自动化系统。本文还提出了采用中间件技术来解决电信MIS建设中数据异构的问题 ,结果发现基于XML的中间件技术很好地实现了数据的共享和集成。同时基于B/S模式的电信MIS对实现电信企业管理水平与运行模式的发展具有重大意义     

基于软件体系结构的反射式中间件研究

Internet为分布应用提供了一种开放、动态的运行环境,这要求分布应用的主要基础设施中间件能够支持运行时查看并调整平台内部状态和行为,由此产生了反射式中间件.目前的反射式中间件研究与实践存在3个不足:注重系统局部或单个实体的反射而缺乏全局视图;注重中间件平台内部功能的反射,而对上层应用的反射不够;集中于CORBA平台,而对J2EE平台的反射性研究较少.介绍了一个反射式的J2EE应用服务器PKUAS.基于构件化的平台内部体系结构,PKUAS引入软件体系结构作为全局视图以实现反射体系对系统整体的表示和控制,作为J2EE应用服务器,PKUAS可反射底层平台以及上层EJB构件.同时,以PKUAS实时监控工具为例,探讨了如何利用基于软件体系结构的反射体系管理整个系统,并给出了PKUAS与其他几种反射式中间件的比较.该工作有效地解决了现阶段反射式中间件研究的不足,提高了反射式中间件的实用性.     

自主构件自适应策略的在线定制及动态评估

开放分布式环境下自适应软件的研究已引起学术界、工业界的广泛关注.但分布在网络上的软件实体是由不同的组织独立开发并部署的,它们代表各自的组织(或所有者)自主地采取行动,在构造分布式环境下的自适应系统时,不能再将构成单元视为被动的受管对象,而应将其建模为具有主动行为能力的计算实体,并在这一层面设计和封装系统的自适应逻辑.然而,在现阶段对于自主计算实体的研究中,大多缺乏对于自适应策略的动态加载和动态演化的支持.提出了一种支持策略动态加载的自主构件模型,使得自主构件能够在运行时习得新的自适应策略和行为,实现了一种基于质量运行时动态评估的自主构件的自适应机制,使得自主构件能够自行评估自适应策略的优劣并选择最佳的策略加以适应,在保证自身目标得以实现的同时,提高了服务质量.另外,还详细描述了自主构件的实现方案及其运行支撑,通过实验展示了自主构件基于质量动态评估的自适应过程以及自适应策略的动态加载过程.     

Simulation-based analysis of middleware service impact on system reliability: Experiment on Java application server

Being a popular runtime infrastructure in the era of Internet, middleware provides more and more services to support the development, deployment and management of distributed systems. At the same time, the reliability of middleware services has a significant impact on the overall reliability of the system. Different services have different impacts and different service fault-tolerance solutions have different costs and risks. Therefore, the identification of the services that greatly affect the whole system reliability is the major obstacle to achieving reliable middleware-based systems. In this paper, we present an analytical framework to automatically reason and quantify such impacts when deploying the target system. In this framework, faults are represented by exceptions in modern programming languages; service failures are simulated by software fault injection; reliability impacts are measured by scenarios. This framework is demonstrated on multiple JEE application servers, including JBoss, JonAS and PKUAS. The experiments on two JEE blueprint applications, namely JPS and ECperf, show the feasibility, the applicability and the usability of this framework.     

Application-level QoS control for video-on-demand

User requirements and device heterogeneity call for Web services with differentiated quality of service (QoS). In particular, services with response-time constraints, such as video-on-demand (VoD), require the differentiation, control, and dynamic adaptation of QoS. Service providers and network operators need methodologies and mechanisms for managing runtime QoS. Using mobile agent technology, the ubiQoS middleware supports QoS tailoring and adaptation of video-on-demand flows in response to user preferences and terminal properties. The design, implementation, and deployment of QoS-aware Internet services can significantly benefit from a middleware approach at the application level. Our experimental results show the feasibility of application-level middleware solutions based on code mobility for Internet VoD services with differentiated QoS.     

Coordinated Recovery of Middleware Services:A Framework and Experiments

Being the most popular runtime infrastructure for distributed systems, middleware can be viewed as a collection of common services. Since the development, deployment and maintenance of distributed systems rely largely on middleware services, the failure of middleware services puts a significant impact on the reliability and availability of the whole system. Though recovery-based fault tolerance is an effective way to improve the reliability of middleware services, it is far away from practice mainly because of the high complexity and cost of the recovery of correlated failures between interdependent services. In this paper,a framework for detecting and recovering the correlated failures of middleware services in an automated way is presented. First, the problem is investigated from two perspectives, i.e.,analyzing the role and impact of middleware services and illustrating a set of correlated failures in J2EE standard services as motivating examples. Then, a general coordinated recovery model is constructed with the elements necessary and su±cient for detecting and recovering correlated failures in middleware services. The supporting framework is demonstrated on three J2EE application servers, i.e., PKUAS, JBoss and JOnAS, one by one without fundamental modifications. Finally, based on the three enhanced application servers, many cases on J2EE common services, including the transaction service, database service, naming and directory service, security service and messaging service, are studied. The experiment results show the effectiveness and applicability of the framework presented in this paper.     

Toward Internet distributed computing

Emerging Internet uses-including peer-to-peer and grid computing-provide both a glimpse of and the impetus for evolving the Internet into a distributed computing, platform of unprecedented scale. Taking a longer view, the authors consider what would be needed to make the Internet an application-hosting platform: a networked, distributed counterpart of the hosting environment traditional operating systems provide to applications within a single node. The foundation of their proposed approach is to disaggregate and virtualize individual system resources as services that can be described, discovered, and dynamically configured at runtime to execute an application.     

REED: Flexible rule based programming of wireless sensor networks at runtime

Wireless Sensor Networks (WSNs) have emerged as an enabling technology for a variety of distributed applications. WSN middleware eases the development of these applications by providing a uniform programming environment. In this paper we present a rule based approach called REED (Rule Execution and Event Distribution) and describe how it supports flexible programming of WSNs at runtime. Indeed REED is required by the nature of its project setting to allow runtime programming. We demonstrate that by combining this runtime programmability with rules in an event, condition, action format we can support a range of paradigms, including Publish-subscribe and data aggregation algorithms. Current WSN middleware solutions have limited on-line programmability support so the applications cannot re-configure their WSNs while operational. Yet the runtime nature of the prototype requires both the distribution of rules and the events that trigger them so we also describe the rule management approach used to support the rule distribution; in particular a novel rule merging and filtering algorithm is described. The paper reports on the results gained from a REED prototype system constructed in our laboratory using Gumstix.     

基于强化学习的自适应中间件在线更新机制研究

自适应中间件框架一般根据预先定义的策略、按照监控、分析、决策、执行的流程实现对开放可变系统的闭环控制。但是,传统的自适应框架基于离线的闭环控制,即在提供自适应服务的同时,自身的决策模型不能随实时的环境变化而更新。针对该问题提出一种基于强化学习的自适应中间件的在线更新方案,解决自适应策略的冲突消解、系统实时效用评估问题,并设计一种基于强化学习的自适应策略在线学习更新方法,增强了自适应中间件的智能性、灵活性和应变能力。最后实现了相应的支撑系统OUSAM并在其上验证了该机制的有效性和可行性。