分布式工作流执行服务的设计与实现

工作流执行服务的实现方案是实施工作流技术最为关键的一个方面,工作流管理系统的应用特点决定了它必须与各种分布的、异构的应用进行通信或与其集成。为了给用户提供透明的工作流执行服务而隐藏工作流执行服务实现的复杂性,文章提出了一种具有三层层次结构的工作流执行服务实现方案,其中的分布式通信服务层由通信中间件实现,使开发者无需关心程序间通信的复杂性,从而将精力放在解决业务问题和优化业务逻辑方面,提高了应用开发的效率。     

基于SIP协议非语音信息扩展的应用研究

利用SIP事件通告机制这一扩展,提出了一种基于SIP的VoIP非语音信息扩展的应用方案,描述了该方案的设计原理,讨论了一些方案实现的技术要点.该设计方案结合了XML技术,结构清晰,故具有较强的扩展性.在VoIP系统中,该方案实现的扩展功能使用户了解当前其他用户的通信状态,避免了一些呼叫事故的发生.     

改进的轻型CORBA事件服务的实现

CORBA事件服务提供了ORB之间异步、多目的通信方式.但标准的事件服务规范过于繁杂,服务质量也有待改进.根据项目应用需求,对事件规范进行了扩充,引入了对事件信道进行管理的模块,同时对标准事件服务规范中的类型事件特征进行删减.然后,基于国内惟一的开源CORBA实现--Orbas,通过代理的设计模式,实现了一个轻型的事件服务,并且在接口级和应用程序级实现对QoS的提高.结果表明,该事件服务可以作为项目的消息传递中间件的底层通信模块,完成分布式对象之间的异步、多目通信.     

一个基于事件驱动的面向服务计算平台

基于请求/响应调用模型的面向服务体系结构(Service-Oriented Architecture,SOA)的实现存在通信耦合程度高,协同能力不足的问题.事件驱动体系结构特别适合于松耦合通信和应用需要感知支持的环境.在面向服务的计算平台中提供事件驱动支持,可满足计算平台的松耦合通信与协同需求.文中给出了面向服务计算平台中事件驱动的框架,针对需高效处理事件流上复合事件的需求,在框架中设计了基于SEDA模型的并发事件处理与基于事件代数的事件流处理机制.在事件代数中给出了上下文语义和相应的检测算法,以实现高效事件流处理.实验表明,设计的事件驱动面向服务计算平台具有松耦合通信、协同计算、高效事件流处理和复合事件处理的特点,适应了目前动态多变的大规模分布式计算环境的需求,有着广阔的应用前景.     

基于CORBA事件服务的分布式对象组件设计与实现

该文在介绍事件服务机制的基础上,将CORBA事件服务封装成COM组件。利用此组件能够有效实现分布式对象组件设计,解决组件对象之间的通信问题,使分布式系统中的对象解耦。声纳测距传感器系统是一个分布式对象组件应用实例,具体验证了所提出的设计思想和方案是切实可行的。设计完成的应用COM组件可用于分布式控制系统。     

基于CORBA的分布实时事件管理技术研究

基于事件的通信是许多分布系统进行异步交互的重要途径 .传统的分布事件管理机制既无法解决分布应用的异构性、复杂性和集成性 ,又无法充分支持实时环境 .分布对象计算的主流技术 CORBA是解决前一个难题的最佳手段 ,但标准的 CORBA事件服务又缺乏对实时应用的支持 .为此 ,本文研究了事件通信在分布实时环境中呈现出的新特性 ,分析了 CORBA事件服务的不足 ,提出了基于 CORBA的分布实时事件管理技术 .通过实时化标准的 CORBA事件服务 ,设计实现了 DREAMS系统 ,为 CORBA在实时领域的应用推广作出了有意义的尝试 .     

基于Web服务的证书验证服务模型的设计与实现

目前在PKI应用中,存在对计算能力和通信能力受限的客户端的支持不够及PKI应用的不兼容等制约PKI发展的问题。为了解决上述两个问题,文中提出了一种基于Web服务的独立证书验证服务模型。该模型将繁重的证书验证计算从证书用户端剥离,有效地降低了对证书用户的计算和通信能力的要求。该模型采用了与平台无关的特性Web服务技术,适应多种PKI应用平台,同时为解决了不同PKI应用的互操作问题提出较为完整的实现方案。     

一种Web服务安全通信机制的研究与实现

随着Web服务技术与应用的发展，Web服务安全问题日益突出。Web服务安全通信要求保证应用层SOAP消息的安全传输，而现有的安全传输方案，如SSL，TLS等不适用于应用层的消息安全保护，无法满足上述要求。针对Web服务应用模式，提出了一种基于XML安全技术的Web服务安全通信机制，利用安全会话实现了较高的实体认证安全性和安全通信效率，并为此设计和实现了保证应用层SOAP消息安全传输的SOAPSec系统。该机制具有灵活性和可扩展性，可满足典型Web服务应用场景下的安全通信需求。     

基于CORBA的实时事件服务的研究与实现

在分布式环境下，事件服务体现为事件的提供者和消费者之间实现灵活的异步或群组通信的机制。在探讨了CORBA中的事件服务及其不足的基础上，讨论了扩展事件服务的实时特性的总体框架和其实时性能设计，并具体实现了一个基于CORBA的分布式实时事件服务(DRES)。测试结果表明该服务能满足实时应用的要求。     

DDS在SCA系统中的应用

针对基于软件通信体系结构(SCA)的通信系统存在着实时性不高、冗余度较大、无法故障恢复等不足,将数据分发服务(DDS)技术引入到SCA架构中,形成了一种扩展方案.在完全保持SCA规范兼容的前提下,用DDS作为波形组件间的传输手段,有效地提高了基于SCA的通信系统的实时性,降低了系统的冗余度,实现了单个软件模块的动态重构.此方案已经在某仿真通信系统中得到了成功的应用.     

Strategic Replication of Video Files in a Distributed Environment

The per service cost has been a serious impediment to wide spread usage of on-line digital continuous media service, especially in the entertainment arena. Although handling continuous media may be achievable due to technology advances in the past few years, its competitiveness in the market with existing service type such as video rental is still in question. In this paper, we propose a model for continuous media service in a distributed infrastructure which has a video warehouse and intermediate storages connected via a high speed communication network, in an effort to reduce the resource requirement to support a set of service requests. The storage resource and network resource to support a set of requests should be properly quantified to a uniform metric to measure the efficiency of the service schedule. We developed a cost model which maps the given service schedule to a quantity. The proposed cost model is used to capture the amortized resource requirement of the schedule and thus to measure the efficiency of the schedule. The distributed environment consists of a massive scale continuous media server called a video warehouse, and intermediate storages connected via a high speed communication network. An intermediate storage is located in each neighborhood, and its main purpose is to avoid the repeated delivery of the same file to a neighborhood. We consider a situation where a request for a video file is made sometime in advance. We develop a scheduling algorithm which strategically replicates the requested continuous media files at the various intermediate storages.     

Algorithms for subsequence combinatorics

A subsequence is obtained from a string by deleting any number of characters; thus in contrast to a substring, a subsequence is not necessarily a contiguous part of the string. Counting subsequences under various constraints has become relevant to biological sequence analysis, to machine learning, to coding theory, to the analysis of categorical time series in the social sciences, and to the theory of word complexity. We present theorems that lead to efficient dynamic programming algorithms to count (1) distinct subsequences in a string, (2) distinct common subsequences of two strings, (3) matching joint embeddings in two strings, (4) distinct subsequences with a given minimum span, and (5) sequences generated by a string allowing characters to come in runs of a length that is bounded from above.     

Decentralized multi-dimensional alert correlation for collaborative intrusion detection

The growth in coordinated network attacks such as scans, worms and distributed denial-of-service (DDoS) attacks is a profound threat to the security of the Internet. Collaborative intrusion detection systems (CIDSs) have the potential to detect these attacks, by enabling all the participating intrusion detection systems (IDSs) to share suspicious intelligence with each other to form a global view of the current security threats. Current correlation algorithms in CIDSs are either too simple to capture the important characteristics of attacks, or too computationally expensive to detect attacks in a timely manner. We propose a decentralized, multi-dimensional alert correlation algorithm for CIDSs to address these challenges. A multi-dimensional alert clustering algorithm is used to extract the significant intrusion patterns from raw intrusion alerts. A two-stage correlation algorithm is used, which first clusters alerts locally at each IDS, before reporting significant alert patterns to a global correlation stage. We introduce a probabilistic approach to decide when a pattern at the local stage is sufficiently significant to warrant correlation at the global stage. We then implement the proposed two-stage correlation algorithm in a fully distributed CIDS. Our experiments on a large real-world intrusion data set show that our approach can achieve a significant reduction in the number of alert messages generated by the local correlation stage with negligible false negatives compared to a centralized scheme. The proposed probabilistic threshold approach gains a significant improvement in detection accuracy in a stealthy attack scenario, compared to a naive scheme that uses the same threshold at the local and global stages. A large scale experiment on PlanetLab shows that our decentralized architecture is significantly more efficient than a centralized approach in terms of the time required to correlate alerts.     

Using a preamble to increase presence in digital virtual environments

Immersion in a digital virtual environment (DVE) increases the likelihood that individuals will feel present in the DVE and hence respond as they would in a similar physically grounded environment. Previous research utilizing high-fidelity technology has demonstrated that by starting a virtual experience in a virtual replica of the immediate physical environment, presence is increased. The purpose of this study was to determine whether utilizing such a transitional environment to increase presence could be replicated on a significantly less immersive system—a 2D desktop monitor with mouse and keyboard for navigation. Participants began their DVE experience either in a “preamble” DVE made to look like the surrounding physical laboratory space, or in a novel DVE (i.e., a house). Then, they were given verbal instructions to leave their respective environments and told to go up a set of stairs to explore a museum. Afterward, they reported levels of immersion and presence in the latter DVE. Results demonstrated that entering a target DVE via a familiar “preamble” environment increased perceptions of reality judgment of the virtual experience, perceptions of possibility to act, and levels of presence. These results suggest that incorporating a familiar digital preamble environment as a prelude to the target DVE enables DVE designers and enthusiasts to increase presence without having to invest in more expensive hardware, but it could also augment existing immersive technology. Their efficacy may be because they offer a gradual transition into the virtual world, such that the familiarity eases users into the novel experience.     

Asymptotically stable walking for biped robots: analysis viasystems with impulse effects

Biped robots form a subclass of legged or walking robots. The study of mechanical legged motion has been motivated by its potential use as a means of locomotion in rough terrain, as well as its potential benefits to prothesis development and testing. The paper concentrates on issues related to the automatic control of biped robots. More precisely, its primary goal is to contribute a means to prove asymptotically-stable walking in planar, underactuated biped robot models. Since normal walking can be viewed as a periodic solution of the robot model, the method of Poincare sections is the natural means to study asymptotic stability of a walking cycle. However, due to the complexity of the associated dynamic models, this approach has had limited success. The principal contribution of the present work is to show that the control strategy can be designed in a way that greatly simplifies the application of the method of Poincare to a class of biped models, and, in fact, to reduce the stability assessment problem to the calculation of a continuous map from a subinterval of R to itself. The mapping in question is directly computable from a simulation model. The stability analysis is based on a careful formulation of the robot model as a system with impulse effects and the extension of the method of Poincare sections to this class of models     

Visual displays: the highlighting paradox

Office computer users view well over a billion displays in a given year. The savings of only a fraction of a second in the time it takes users to process each display can potentially lead to enormous time and cost savings. In recent research investigators have shown that on average subjects are quicker to find a target option in a highlighted display than in a display without highlighting. Paradoxically, in related research other investigators have shown that subjects are slower to find a target in a highlighted display than in a display without highlighting. In an attempt to resolve this paradox, an additional set of experiments was performed. Results from these experiments suggest that in order to determine whether highlighting will be of benefit, one must know the type of highlighting, the level of highlighting validity, and the probability that subjects attend first to the highlighted options.     

Superposition Based on Watson–Crick-Like Complementarity

In this paper we propose a new formal operation on words and languages, called superposition. By this operation, based on a Watson–Crick-like complementarity, we can generate a set of words, starting from a pair of words, in which the contribution of a word to the result need not be one subword only, as happens in classical bio-operations of DNA computing. Specifically, starting from two single stranded molecules x and y such that a suffix of x is complementary to a prefix of y, a prefix of x is complementary to a suffix of y, or x is complementary to a subword of y, a new word z, which is a prolongation of x to the right, to the left, or to both, respectively, is obtained by annealing. If y is complementary to a subword of x, then the result is x. This operation is considered here as an abstract operation on formal languages. We relate it to other operations in formal language theory and we settle the closure properties under this operation of classes in the Chomsky hierarchy. We obtain a useful result by showing that unrestricted iteration of the superposition operation, where the "parents" in a subsequent iteration can be any words produced during any preceding iteration step, is equivalent to restricted iteration, where at each step one parent must be a word from the initial language. This result is used for establishing the closure properties of classes in the Chomsky hierarchy under iterated superposition. Actually, since the results are formulated in terms of AFL theory, they are applicable to more classes of languages. Then we discuss "adult" languages, languages consisting of words that cannot be extended by further superposition, and show that this notion might bring us to the border of recursive languages. Finally, we consider some operations involved in classical DNA algorithms, such as Adleman's, which might be expressed through iterated superposition.     

FSfRT: FORECASTING SYSTEM FOR RED TIDES. A HYBRID AUTONOMOUS AI MODEL

A hybrid neuro-symbolic problem-solving model is presented in which the aim is to forecast parameters of a complex and dynamic environment in an unsupervised way. In situations in which the rules that determine a system are unknown, the prediction of the parameter values that determine the characteristic behavior of the system can be a problematic task. In such a situation, it has been found that a hybrid case-based reasoning system can provide a more effective means of performing such predictions than other connectionist or symbolic techniques. The system employs a case-based reasoning model that incorporates a growing cell structures network, a radial basis function network, and a set of Sugeno fuzzy models to provide an accurate prediction. Each of these techniques is used at a different stage of the reasoning cycle of the case-based reasoning system to retrieve historical data, to adapt it to the present problem, and to review the proposed solution. This system has been used to predict the red tides that appear in the coastal waters of the north west of the Iberian Peninsula. The results obtained from experiments, in which the system operated in a real environment, are presented.     

Change in pattern of absenteeism as a result of workplace intervention for personnel support

The aim was to investigate whether a preventive intervention carried out in a predominantly female workplace, that of hospital cleaners (consisting of a group of 97 women), had any effect on patterns of absenteeism. As a background, a model for analysing complex patterns of absenteeism, including sickness absences, was also developed. A further aim was to study the interactions between different forms of absenteeism. Comparison was made with a reference group consisting of employees in the same job category who only received the customary personnel support. For individuals in the intervention group who were < 42 years of age, total absence due to sickness decreased. In a multiple regression analysis, the contribution from the intervention to the decrease was significant at the 5% level. This change was particularly obvious in those who had a previous history of high absence due to sickness. No clear relationship was shown between short-term absenteeism and the interventions applied. For those who were > 42 years, short-term absence decreased for those who had been in the same jobs for a long time. The combination of increased age and experience showed a tendency to enhance this decline in short-term absenteeism due to sickness. For those > 42 years, and who at the same time have a previous history of high absenteeism, long-term absenteeism due to sickness seemed to be increasing. Increased experience tended to reduce this increase in long-term sickness absence. This combination of different effects possibly indicated the presence of a process of selection which determined who remained in the job as opposed to those who did not. An important conclusion is that different forms of absenteeism need to be looked at in parallel, and at the same time multivariate statistical analysis needs to be carried out to determine the different interactions between the factors.