Parallel Algorithm Design for Workstation Clusters
Clusters of workstations connected by local area networks are in common use in many organizations. The combined processing power of these clusters is rarely exploited owing to the lack of suitable parallel algorithms. The paper describes a parallel programming paradigm called supervisor-worker, suitable for the workstation environment, which can be used to speed up the execution of a large class of existing sequential programs. Simple formulae are developed to predict the speed-up of a parallel algorithm developed in this way. The predictions depend on two easily-determined parameters of the sequential program and the characteristic communication cost of the workstation cluster. Consequently, it is possible to estimate the benefits of the parallel program before proceeding with detailed implementation. As an example, the parallel version of a travelling salesman program is developed and the measured speed-up compared with the predicted speed-up.

title: Checking safety properties using compositional reachability analysis
abstract: The software architecture of a distributed program can be represented by a hierarchical composition of subsystems, with interacting processes at the leaves of the hierarchy. Compositional reachability analysis (CRA) is a promising state reduction technique which can be automated and used in stages to derive the overall behavior of a distributed program based on its architecture. CRA is particularly suitable for the analysis of programs that are subject to evolutionary change. When a program evolves, only the behaviors of those subsystems affected by the change need be reevaluated. The technique however has a limitation. The properties available for analysis are constrained by the set of actions that remain globally observable. Properties involving actions encapsulated by subsystems may therefore not be analyzed. In this article, we enhance the CRA technique to check safety properties which may contain actions that are not globally observable. To achieve this, the state machine model is augmented with a special trap state labeled as π. We propose a scheme to transform, in stages, a property that involves hidden actions to one that involves only globally observable actions. The enhanced technique also includes a mechanism aiming at reducing the debugging effort. The technique is illustrated using a gas station system example.

title: Developing a Distributed e-Monitoring System for Enterprise Website and Web Services: An Experience Report with Free Libraries and Tools
abstract: Enterprises value monitoring as it provides dependable e-services, whether it is an interactive Web site or programmatic Web service. However, this task becomes non-trivial when enterprises begin to require support from thousands of servers across geographical areas. How can the communications between a monitoring systems and remote servers be minimized? Could the task be achieved easily based on a readily available technology such as SNMP? How can we monitor thousands of servers powered by, say, Tomcat, which lacks SNMP support? How may a poorly responsive site be identified prior to being reported as a failure by SNMP? In this paper, we propose a unified e-monitoring system that enables system administrators to remotely monitor the health of distributed e-services in both the form of Web site and Web services. We further discuss our implementation experience based on a pragmatic prototype.

title: Exploiting automatic analysis of e-commerce protocols
abstract: While e-commerce continuously grows prosperous, some advantages e-commerce applications claimed haven't really been gained. More seriously, the availability and reliability of these systems are particularly hard to obtain. The e-commerce protocols, as the core of e-commerce applications, ask for new development approach and techniques to be introduced for their highly reliable and safe design and implementation. This paper describes research on synthesis of extended UML formalism and formal verification techniques for automatic development of e-commerce protocols. In this paper, we refine AUML protocol diagrams for visual modeling, and develop algorithm and rules to translate visually modeled e-commerce protocols into formal models that are then validated using model checking. This approach is applied to the design of an e-commerce protocol, NetBill, as example. Our objective is to create tools that enable designers to automatically develop available and reliable e-commerce protocols.

title: Constraint-based negotiation in a multi-agent information system with multiple platform support
abstract: Agent technologies have been deployed to model and implement e-commerce activities as multi-agent information systems (MAIS). Agents provide services to one another for mutual gain on behalf of their users. This paper presents an MAIS infrastructure based on belief-desire-in tension (BDI) agent architecture, constraint technology, and contemporary Web services to facilitate negotiation support. Further, the MAIS infrastructure also supports customizable degree of agent delegation for users on different platforms, with or without agent support. We present a constraint-based negotiation protocol extended for a MAIS environment and detail the required adaptations on different platforms from a three-tier implementation architecture aspect.

title: A Multi-Agent Infrastructure for Mobile Workforce Management in a Service Oriented Enterprise
abstract: With recent advances in mobile technologies and infrastructures, there are increasing demands for the support of mobile workforce management (MWM) across multiple platforms. Mobile users can interact with the MWM system through SMS messages or Web browsers from personal computers, PDA devices, or WAP phones. MWM typically involves tight collaboration, negotiation, and sophisticated business domain knowledge. Therefore, the main challenge of MWM for a service oriented enterprise is the integration of disparate business function for its mobile professional workforce and the management with a unified infrastructure, together with the provision of personalized assistance and automation. These requirements can be facilitated with the use of intelligent software agents, but has not been adequately studied before. As mobile devices become more powerful, intelligent software agents can now be deployed on these devices and hence also subject to mobility. Thus, MWM systems have to accommodate these requirements as well as the support of heterogeneous platforms. In this paper, we formulate a scalable, flexible, and intelligent multi-agent information system (MAIS) infrastructure for MWM with agent clusters in the context of a large service oriented enterprise. Each agent cluster comprise several types of agents to achieve the goal of each phase of the workforce management process, namely, task formulation, matchmaking, brokering, commuting, and service. We evaluate our approach against different stakeholders' perspective.

title: Denial of service against the Domain Name System
abstract: Because many network services rely on the Domain Name System, denial-of-service attacks against it can be particularly damaging. This article analyzes such threats and reviews existing and proposed countermeasures for addressing them.

title: Efficient video similarity measurement with video signature
abstract: The video signature method has previously been proposed as a technique to summarize video efficiently for visual similarity measurements (see Cheung, S.-C. and Zakhor, A., Proc. SPIE, vol.3964, p.34-6, 2000; ICIP2000, vol.1, p.85-9, 2000; ICIP2001, vol.1, p.649-52, 2001). We now develop the necessary theoretical framework to analyze this method. We define our target video similarity measure based on the fraction of similar clusters shared between two video sequences. This measure is too computationally complex to be deployed in database applications. By considering this measure geometrically on the image feature space, we find that it can be approximated by the volume of the intersection between Voronoi cells of similar clusters. In the video signature method, sampling is used to estimate this volume. By choosing an appropriate distribution to generate samples, and ranking the samples based upon their distances to the boundary between Voronoi cells, we demonstrate that our target measure can be well approximated by the video signature method. Experimental results on a large dataset of Web video and a set of MPEG-7 test sequences with artificially generated similar versions are used to demonstrate the retrieval performance of our proposed techniques.

title: Efficient video similarity measurement and search
abstract: We consider the use of meta-data and/or video-domain methods to detect similar videos on the Web. Meta-data is extracted from the textual and hyperlink information associated with each video clip. In the video domain, we apply an efficient similarity detection algorithm called video signature. The idea is to form a signature for each clip by selecting a small number of its frames that are most similar to a set of random seed images. We then apply a statistical pruning algorithm to allow fast detection on very large databases. Using a small ground-truth set, we achieve 90% recall and 95% precision using only 8% of the total number of operations required without pruning. For a database of around 46,000 video clips crawled from the Web, the video signature technique significantly outperforms meta-data in precision and recall. We show that even better performance can be achieved by combining them together. Based on our measurements, each video clip in our database has, on average, 1.53 similar copies.

title: An efficient message authentication scheme for link state routing
abstract: We study methods for reducing the cost of secure link state routing. In secure link state routing, routers may need to verify the authenticity of many routing updates, and some routers such as border routers may need to sign many routing updates. Previous work such as public-key based schemes are very expensive computationally or have certain limitations. This paper presents an efficient solution, based on a detection-diagnosis-recovery approach, for the link state routing update authentication problem. Our scheme is scalable to handle large networks, applicable to routing protocols that use multiple-valued cost metrics, and applicable even, when link states change frequently.

title: An Architecture for an Adaptive Intrusion-Tolerant Server
abstract: We describe a general architecture for intrusion-tolerant enterprise systems and the implementation of an intrusion-tolerant Web server as a specific instance. The architecture comprises functionally redundant COTS servers running on diverse operating systems and platforms, hardened intrusion-tolerance proxies that mediate client requests and verify the behavior of servers and other proxies, and monitoring and alert management components based on the EMERALD intrusion-detection framework. Integrity and availability are maintained by dynamically adapting the system configuration in response to intrusions or other faults. The dynamic configuration specifies the servers assigned to each client request, the agreement protocol used to validate server replies, and the resources spent on monitoring and detection. Alerts trigger increasingly strict regimes to ensure continued service, with graceful degradation of performance, even if some servers or proxies are compromised or faulty. The system returns to less stringent regimes as threats diminish. Servers and proxies can be isolated, repaired, and reinserted without interrupting service.