Glenn S. Wasson

State and events for Web services: a comparison of five WS-resource framework and WS-notification implementations

The Web services resource framework defines conventions for managing state in distributed systems based on Web services, and WS-notification defines topic-based publish/subscribe mechanisms. We analyze five independent and quite different implementations of these specifications from the perspectives of architecture, functionality, standards compliance, performance, and interoperability. We identify both commonalities among the different systems (e.g., similar dispatching and SOAP processing mechanisms) and differences (e.g., security, programming models, and performance). Our results provide insights into effective implementation approaches. Our results may also provide application developers, system architects, and deployers with guidance in identifying the right implementation for their requirements and in determining how best to use that implementation and what to expect with regard to performance and interoperability.

An assistive robotic agent for pedestrian mobility

The goal of this project is to develop a pedestrian mobility aid for the elderly. In order for this type of assistive technology to be useful and accepted by its intended user community, it must enhance the abilities of users, not replace them. This leads to an agent architecture in which the agent must operate without hindering the users ability to take direct action when they choose. In other words, the agent cannot simply be a proxy for the users actions. The agent must select its own goals based on observations of its users actions. This is crucial not only because users may have diminished capacity to explain their actions to an agent, but because the ability of the agent to correctly interpret the users goals is tied to its ability to act while still allowing the user to “feel in control”. We present a mobility aid, i. e. a wheeled walker, which varies its goals and level of activity based on an estimation of its users intentions. The assistive agent often takes no action, allowing the user to be fully in control. When the ease or safety of the users travel is threatened, the agent attempts to influence the users motion based on its belief in the users goal. By varying the degree of autonomy, the walker can adjust to the user as their abilities change from day to day, or hour to hour. This prevents the walker from trying to do too much, allowing the user to feel as if they are in control and not being lead.

Characterization of Infrared Range-Finder PBS-03JN for 2-D Mapping

This paper presents a characterization study of the HOKUYO PBS-03JN Infrared range-finder and compares it to the characterization of the SICK LMS-200 laser range-finder for use in indoor 2-D mapping. Many parameters that could affect the performance of the sensor including warm-up time, divergence of the detection beam, usable detection range in the azimuth, target surface, color, and size properties, incidence angle at the target, and the mixed pixels problem have been studied. This characterization, quantification of errors, and 3-D confidence in the distance readings of the sensor is vital for practical applications. These characteristics are compared to the counterpart characteristics of the laser range-finder. The PBS-03JN is a cost effective alternative to laser range-finders in indoor environments. The sensor is attractive due to lower power consumption, and its lightweight.

Support for extensibility and site autonomy in the Legion grid system object model

Grid computing is the use of large collections of heterogeneous, distributed resources (including machines, databases, devices, and users) to support large-scale computations and wide-area data access. The Legion system is an implementation of a software architecture for grid computing. The basic philosophy underlying this architecture is the presentation of all grid resources as components of a single, seamless, virtual machine. Legions architecture was designed to address the challenges of using and managing wide-area resources. Features of the architecture include: global, shared namespaces; support for heterogeneity; security; wide-area data sharing; wide-area parallel processing; application-adjustable fault tolerance; efficient scheduling and comprehensive resource management. We present the core design of the Legion architecture, with focus on the critical issues of extensibility and site autonomy. Grid systems software must be extensible because no static set of system-level decisions can meet all of the diverse, often conflicting, requirements of present and future user communities, nor take best advantage of unanticipated future hardware advances. Grid systems software must also support complete site autonomy, as resource owners will not turn control of their resources over to a dictatorial system.

Architectural Foundations of WSRF NET

State management has always been an underlying issue for large-scale distributed systems, but only recently has it been brought to the forefront of Grid computing with the introduction of the Web Services Resource Framework (WSRF) and its companion, WS-Notification. WSRF advocates standardized approaches for client exposure to and potential manipulation of stateful services for Grid computing; however, these arguments and their long-term implications have been difficult to assess without a concrete implementation of the WSRF specifications. This paper describes the architectural foundations of WSRF.NET, which is an implementation of the full set of specifications for WSRF and WS-Notification on the Microsoft .NET Framework. To our knowledge, the observations and lessons learned from the design and implementation of WSRF.NET provide the first evaluation of the WSRF approach. A concrete example of the design, implementation, and deployment of a WSRF-compliant service and its accompanying WSRF-compliant client are used to guide the discussion. While the potential of WSRF and WS-Notification remains strong, initial observations are that there are many challenges that remain to be solved, most notably the implied programming model derived from the specifications, particularly the complexity of service side and client code and the complexity of WS-Notification.

An early evaluation of WSRF and WS-Notification via WSRF.NET

The Web Services Resource Framework (WSRF) and its companion WS-Notification were introduced in January 2004 as a new model on which to build grids. This paper contains early observations made while implementing the full suite of WSRF and WS-Notification specifications on the Microsoft .NET Platform. While the potential of WSRF and WS-Notification remains strong, initial observations are that there are many challenges that remain to be solved, most notably the implied programming model derived from the specifications, particularly the complexity of service-side and client-code and the complexity of WS-Notification.

Evaluation of UDDI as a provider of resource discovery services for OGSA-based grids

Grid computing involves networks of heterogeneous resources working in collaboration to solve problems that cannot be addressed by the resources of any one organization. A pervasive problem for grid users is how best to discover the resources they need given dynamic grid environments. UDDI, the universal description, discovery and integration framework, is an OASIS standard for publishing and querying discovery information for Web services, which to date, has received surprisingly little analysis as a discovery mechanism for Web service-based grids, e.g. those based on the open grid services architecture (OGSA). This work identifies issues that must be addressed in order to make UDDI meet the requirements of OGSA discovery. We examine the performance implications of these issues using a freely available implementation of UDDI version 2. Based on our experimental results, we conclude that UDDI can be used for OGSA discovery, but the cost may be prohibitive for large grids.

Toward seamless grid data access: design and implementation of GridFTP on .NET

To date, only Linux/UNIX-based hosts have been participants in the Grid vision for seamless data access, because the necessary Grid data access protocols have not been implemented on Windows. As part of our larger effort at the University of Virginia to make the Windows platform a first-class participant in all aspects of grids, this paper describes our experiences and lessons learned while implementing GridFTP on the Microsoft .NET Framework. Our implementation not only supports major extensions of GridFTP v1, it also uniquely implements some features of GridFTP v2 and introduces a new transfer mode specifically designed for transfer of large collection of small files. Our measured performance is comparable to GT4 GridFTP on both single and parallel streams transfer and more efficient than GT4 GridFTP on directory tree transfer. We also identify issues specific to the .NET Framework/Windows platform with regard to security and we identify limitations of current GridFTP protocol. To our knowledge, the work described in this paper is the first comprehensive and evaluated implementation of GridFTP on .NET.

Passive derivation of basic walker-assisted gait characteristics from measured forces and moments

This work describes a method that passively assesses basic walker-assisted gait characteristic, including heel strikes, toe-off events, as well as stride time, double support and right & left single support phases using only force-moment measurements from the walkers handles. The passively derived gait characteristics were validated against motion capture gait analysis and showed good correlations. This research is part of an effort that aims to identify user intent, from measuring forces and moments exerted on the handles of the walker as well as from perceiving the environment, and to incorporate identified intent into a passive shared steering control system for the walker. The primary focus of the work leading to This work is to identify the double support phase, and to engage the steering control at the beginning of this phase to maximize the users stability. However, the application of the method presented and the instrumented walker can be extended to longitudinal outside the lab Gait assessment.

Integrating active perception with an autonomous robot architecture

Abstract Today’s robotics applications require complex, real-time, high-bandwidth sensor systems. Although many such systems have been developed, integrating them into an autonomous agent architecture remains an area of active research. We have integrated an active stereo vision system with an autonomous agent architecture using a system of perceptual memory. Perceptual memory is an important class of memory because it is designed for the ‘behavior-based’ portion of the agent’s architecture, and not the deliberative portion. This memory maintains current and recent task-dependent perceptual information, as well as expectations about the agent’s immediate environment. Our system of perceptual memory is composed of visual primitives from our stereo system, called proximity spaces. Each proximity space represents a virtual fovea or locus of the agent’s attention. As an application, we present a robot that uses our system of perceptual memory and proximity spaces to ‘attend to’ multiple humans in a complex and unstructured indoor environment.