A sound and complete algorithm for distributed commerce transactions

Summary. In a multi-party transaction (also called a distributed commerce transaction) agents face risks from dealing with untrusted agents. These risks are compounded in the face of deadlines, e.g., an agent may fail to deliver purchased goods by the time the goods are needed. We characterize the risks, and present a distributed algorithm that mitigates these risks, by using pairwise exchanges and trusted intermediaries. The algorithm generates a safe sequence of actions that completes a commerce transaction without risk, if such a sequence exists. We show that the algorithm is sound (produces only safe multi-agent action sequences) and complete (finds a safe sequence whenever one exists). The initial restriction of guaranteeing safety even when none of the principals trusts another can be relaxed in some cases, so we show how to handle principals that do trust each other and interact directly rather than through a trusted intermediary. Received: September 1997 / Accepted: December 1998     

Applying artificial intelligence to virtual reality: Intelligent virtual environments

Research into virtual environments on the one hand and artificial intelligence and artificial life on the other has largely been carried out by two different groups of people with different preoccupation and interests, but some convergence is now apparent between the two fields. Applications in which activity independent of the user takes place- involving crowds or other agents- are beginning to be tackled, while synthetic agents, virtual humans, and computer pets are all areas in which techniques from the two fields require strong integration. The two communities have much to learn from each other if wheels are not to be reinvented on both sides. This paper reviews the issues arising from combining artificial intelligence and artificial life techniques with those of virtual environments to produce just such intelligent virtual environments. The discussion is illustrated with examples that include environments providing knowledge to direct or assist the user rather than relying entirely on the user's knowledge and skills, those in which the user is represented by a partially autonomous avatar, those containing intelligent agents separate from the user, and many others from both sides of the area.     

Virtual environments and ergonomics: needs and opportunities

Although based on a still immature technology, virtual environments appear to have potential for applications in industry, commerce, medicine and education. The role of ergonomics will be in development of improved virtual environment interfaces and in enabling better utilization of the technology through specifying user needs and requirements and developing evaluation methodologies. By extension, ergonomists will also be involved in building virtual environments for use in areas of ergonomics activity such as workplace layout, interface design, procedures testing, education and training. This paper overviews virtual environment attributes and capabilities and proposes a framework for their specification, development and evaluation, before summarizing current ergonomics research issues. Current work on participant side effects is summarized. A strong case is made for the potential value of ergonomics for virtual environments and vice versa.     

Adaptation in virtual environments: conceptual framework and user models

When interacting in a virtual environment, users are confronted with a number of interaction techniques. These interaction techniques may complement each other, but in some circumstances can be used interchangeably. Because of this situation, it is difficult for the user to determine which interaction technique to use. Furthermore, the use of multimodal feedback, such as haptics and sound, has proven beneficial for some, but not all, users. This complicates the development of such a virtual environment, as designers are not sure about the implications of the addition of interaction techniques and multimodal feedback. A promising approach for solving this problem lies in the use of adaptation and personalization. By incorporating knowledge of a user’s preferences and habits, the user interface should adapt to the current context of use. This could mean that only a subset of all possible interaction techniques is presented to the user. Alternatively, the interaction techniques themselves could be adapted, e.g. by changing the sensitivity or the nature of the feedback. In this paper, we propose a conceptual framework for realizing adaptive personalized interaction in virtual environments. We also discuss how to establish, verify and apply a user model, which forms the first and important step in implementing the proposed conceptual framework. This study results in general and individual user models, which are then verified to benefit users interacting in virtual environments. Furthermore, we conduct an investigation to examine how users react to a specific type of adaptation in virtual environments (i.e. switching between interaction techniques). When an adaptation is integrated in a virtual environment, users positively respond to this adaptation as their performance significantly improve and their level of frustration decrease.     

Constructing communication subgraphs and deriving an optimalsynchronization interval for distributed virtual environmentsystems

The author considers problems of constructing a communication subgraph and deriving an optimal synchronization interval for a distributed virtual environment system (DVE). In general, a DVE system is a distributed system which allows many clients who are located in different parts of the network to concurrently explore and interact with each other under a high resolution, 3D, graphical virtual environment. Each client in a DVE system is represented by an avatar in the virtual environment, and each avatar can move and interact freely in the virtual environment. There are many challenging issues in designing a cost-effective DVE system. The article addresses two important design issues, namely: 1) how to construct a communication subgraph which can efficiently carry traffic generated by all clients in a DVE system, and 2) how to guarantee that each participating client has the same consistent view of the virtual world. In other words, if there is an action taken by an avatar or if there is any change in the state of an object in the virtual world, every participating client will be able to view the change. To provide this consistent view, a DVE system needs to perform synchronization actions periodically, We present several algorithms for constructing a communication subgraph. In the subgraph construction, we try to reduce the consumption of network bandwidth resources or reduce the maximum delay between any two clients in a DVE system. Based on a given communication subgraph, we then derive the optimal synchronization interval so as to guarantee the view consistency among all participating clients. The derivation of the optimal synchronization interval is based on the theory of Markov chains and the fundamental matrix     

Store selection criteria and sales prediction in virtual worlds

Virtual worlds (VWs) have emerged as a new context for gaming, collaboration, social networking but also commercial activity. This paper focuses on the latter, and investigates how consumers behave in this virtual context when selecting stores they visit or buy from. The paper explores store selection criteria in virtual world stores and extends earlier research in both offline and online commercial environments, taking into account the novel IT capabilities that VWs exploit. Theoretical insights drawn from the marketing and information systems literature have been used to guide the design of a survey conducted in the virtual world Second Life. In addition to identifying the factors influencing store selection, the paper investigates how these differ between shoppers and non-shoppers, and identifies the factors that affect the amount of money spent in virtual world shopping environments. The findings suggest that “Core Store Features” and “Security and Privacy” constitute the most important store selection factors in virtual environments and that sales in VWs are predicted by the frequency of visiting and the time spent within VWs’ stores. Building on these findings, the paper discusses theoretical and practical implications and further research perspectives in the context of (3D) online commerce.     

Postural instability and motion sickness in a virtual moving room

OBJECTIVE: We examined motion sickness in an oscillating virtual environment presented via a video projector system. BACKGROUND: Visible oscillation of the physical environment is known to induce both postural instability and motion sickness, but it cannot be assumed that the same phenomena will occur in a virtual simulation of such motion. METHOD: Standing participants (3 men and 9 women, 20-22 years of age) were exposed to oscillation of a virtual room. The stimulus was a computer-generated simulation of a laboratory device that is known to induce postural instability and motion sickness. Participants viewed the simulation for up to 40 min and were instructed to discontinue if they experienced symptoms of motion sickness. RESULTS: Motion sickness incidence (42%) did not differ from that in studies using the corresponding physical moving room. Prior to motion sickness onset, the sick group exhibited changes in movement, relative to the well group, as predicted by the postural instability theory of motion sickness. Differences in movement between the sick and well groups developed over time, in contrast with previous studies using physical moving rooms, in which such movement differences have not evolved. CONCLUSION: The results indicate that changes in postural activity precede motion sickness that is induced by an oscillating virtual environment, but they also reveal differences in postural responses to virtual and physical motion environments. APPLICATION: Potential applications of this research include recommendations for the use of virtual environments as models for perception and action in physical environments.     

Standards and verification for fair-exchange and atomicity in e-commerce transactions

Electronic commerce can be defined as the conduct of commerce in goods and services, with the assistance of telecommunications and telecommunications-based tools. The economic growth potential of e-commerce is extraordinary—but so are the challenges that lie on the path toward success. One of the more pressing challenges is how to ensure the integrity and reliability of the transaction process: key aspects being fair-exchange and atomicity assurance.This paper delineates an extended fair-exchange standard, which includes atomicity assurance, intended for a wide audience including e-commerce designers, managers, users, and auditors. We demonstrate how such a standard prevents or mitigates important e-commerce concerns. To bridge theory with practice, we illustrate how the application of model checking can be used to verify the correctness of the implementation of e-commerce protocols to prevent the failure of such protocols when unforeseen circumstances occur.     

Performance analysis of long-lived cooperative transactions in active DBMS

Active database management systems (ADBMS) are used in different application domains and especially for cooperative and long duration activity management. This paper deals with performance analysis of long-lived cooperative transaction processing in an ADBMS. We first briefly discuss NP-QuadLock – a concurrency control scheme for cooperative and long durational transactions in ADBMS. A restricted version of NP-QuadLock named 2L-QuadLock has been used for simulation. We have modeled such an ADBMS supporting 2L-QuadLock scheme by a queuing model. The failure of the transactions running in such systems has been modeled by a failure recovery model. We have simulated this model for a transaction processing system serving long-lived and cooperative transactions. We also discuss some important emerging application scenarios, where the proposed cooperative complex transaction mechanism can be used (e.g. 3G-service environment, ubiquitous computing environment, feature composition in intelligent network environment, multi-site and multi-domain web-services).

An important objective of our work is to analyze quantitatively (a) the performance penalty on the system due to the partial abort, the number of locks held by a transaction, the number of states of the transactions, and (b) the gain in the performance of the system with the cooperation semantics proposed in 2L-QuadLock concurrency control mechanism. We have analyzed the effect of various parameters such as partial abort rate, cooperation rate, number of locks held by a transaction, multiprogramming level, on the performance metrics such as average service time, average saga length and the degree of compensation. Later, we characterize the application scenarios based on some important simulation parameters, and discuss the application performance needs for each of the application scenarios. The required performance parameters that need to be used for these application scenarios and the corresponding performance results using 2L-QuadLock are also discussed.     

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.     

Global scheduling for flexible transactions in heterogeneousdistributed database systems

A heterogeneous distributed database environment integrates a set of autonomous database systems to provide global database functions. A flexible transaction approach has been proposed for the heterogeneous distributed database environments. In such an environment, flexible transactions can increase the failure resilience of global transactions by allowing alternate (but in some sense equivalent) executions to be attempted when a local database system fails or some subtransactions of the global transaction abort. We study the impact of compensation, retry, and switching to alternative executions on global concurrency control for the execution of flexible transactions. We propose a new concurrency control criterion for the execution of flexible and local transactions, termed F-serializability, in the error-prone heterogeneous distributed database environments. We then present a scheduling protocol that ensures F-serializability on global schedules. We also demonstrate that this scheduler avoids unnecessary aborts and compensation     

The virtual playground: an educational virtual reality environment for evaluating interactivity and conceptual learning

The research presented in this paper aims at investigating user interaction in immersive virtual learning environments, focusing on the role and the effect of interactivity on conceptual learning. The goal has been to examine if the learning of young users improves through interacting in (i.e. exploring, reacting to, and acting upon) an immersive virtual environment (VE) compared to non-interactive or non-immersive environments. Empirical work was carried out with more than 55 primary school students between the ages of 8 and 12, in different between-group experiments: an exploratory study, a pilot study, and a large-scale experiment. The latter was conducted in a virtual environment designed to simulate a playground. In this “Virtual Playground,” each participant was asked to complete a set of tasks designed to address arithmetical “fractions” problems. Three different conditions, two experimental virtual reality (VR) conditions and a non-VR condition, that varied the levels of activity and interactivity, were designed to evaluate how children accomplish the various tasks. Pre-tests, post-tests, interviews, video, audio, and log files were collected for each participant, and analysed both quantitatively and qualitatively. This paper presents a selection of case studies extracted from the qualitative analysis, which illustrate the variety of approaches taken by children in the VEs in response to visual cues and system feedback. Results suggest that the fully interactive VE aided children in problem solving but did not provide a strong evidence of conceptual change as expected; rather, it was the passive VR environment, where activity was guided by a virtual robot, that seemed to support student reflection and recall, leading to indications of conceptual change.     

Future multimedia user interfaces

No matter how powerful or elegant the technologies underlying multimedia computing, it is the user interface that ultimately determines how these systems will be used. We provide an overview of two emerging areas of user-interface research that will play major roles in future multimedia systems: virtual environments and ubiquitous computing. We discuss what they are and why they are important, and describe their relationship to current multimedia systems. While mouse and window-based user interfaces provide access to 2D graphics, video, and sound, virtual environments not only involve interactive 3D graphics, but further address all our senses through the use of spatial audio, haptics, and other modalities. While it is still a research goal to provide high-throughput video on demand, ubiquitous computing will require that multimedia network infrastructure also support extremely low-latency interaction among large numbers of mobile wireless users. To arrive at an understanding of the needs, capabilities, and potential of these new paradigms, we introduce their terminology and technology, and explain the basic system architectures being explored, leading up to a discussion of key current research issues and future directions.     

Predicting users' return to virtual worlds: a social perspective

Virtual worlds or three‐dimensional computer‐based simulated environments have received considerable attention as platforms for entertainment, education and commerce. In contrast to a web site, for example, where a user interacts with a two‐dimensional site, virtual worlds provide a platform in which users can interact with other individuals, sometimes including strangers, within three‐dimensional environments. Virtual worlds afford a form of ‘socialness’ unlike many other technologies, often motivating a user – by virtue of these social experiences – to return. Drawing on the Spatial Model of Interaction and Awareness‐Attention Theory, we demonstrate that besides social aspects, which include social awareness and social perception, flow experience, which is the mental state of being fully absorbed and somewhat lost in time, is an essential ingredient in an individual's decision to return to a virtual world. We also demonstrate how characteristics of the technology are linked to the social aspects experienced in virtual worlds. A laboratory study conducted in a virtual world, Second Life, supports our assertions and identifies state predictors of flow that influence individuals' intentions to return to the virtual world environment.     

Adapting grid computing environments dependable with virtual machines: design, implementation, and evaluations

Due to its potential, using virtual machines in grid computing is attracting increasing attention. Most of the researches focus on how to create or destroy a virtual execution environments for different kinds of applications, while the policy of managing the virtual environments is not widely discussed. This paper proposes the design, implementation, and evaluation of an adaptive and dependable virtual execution environment for grid computing, ADVE, which focuses on the policy of managing virtual machines in grid environments. To build a dependable virtual execution environments for grid applications, ADVE provides an set of adaptive policies managing virtual machine, such as when to create and destroy a new virtual execution environment, when to migrate applications from one virtual execution environment to a new virtual execution environment. We conduct experiments over a cluster to evaluate the performance of ADVE, and the experimental results show that ADVE can improve the throughput and the reliability of grid resources with the adaptive management of virtual machines.     

Decision-making in-socio and in-situ: Facilitation in virtual worlds

Past research suggests that “situatedness”, i.e. the context, as well as the social interaction that occurs within it, play an important role in cognitive processes such as learning and decision-making. Thus far, IT tools have been limited in the level and type of situatedness they facilitate. The advent of virtual worlds has changed this. Virtual worlds provide open, three-dimensional platforms for creating and designing real life-like spaces; they also allow for interaction between users in the form of “avatars” in that space. This research study focuses on virtual worlds as platforms for learning and decision-making. We propose a model that explains how individuals in a group learn and make decisions through a process that is influenced by the two unique characteristics of virtual worlds that enable situatedness: the facilitation for designing real life-like spaces, and the facilitation of rich many-to-many interactions.We draw on theories of situated cognition, social cognition, and flow to explicate the influence of these characteristics on the process of learning and decision-making. Data was collected by means of a quasi-experiment in Second Life (SL). Results from this study extend and validate the predictions of situated theories of decision-making within the context of a virtual world environment and suggest guidelines for practitioners who wish to use such environments to support organizational learning and decision-making. Perhaps the most compelling of these is to focus on maximizing the immersion of the individual in the activity by stimulating his or her perceptions of others and activity-related cues in the environment.     

Learning from virtual reality applications in education

This paper presents an overview of the uses of virtual reality in education. It draws particularly on three projects, the West Denton High School in Newcastle, the Human-Computer Interface Technology Laboratory's summer school in Seattle and the Shepard School for children with special needs in Nottingham. In each of these projects, there is distinctive relationship between the learning experience and the experience of virtual worlds. Here, the concern will not be with the pedagogical value of these projects, which have been documented elsewhere, but with the wider contribution that they can make to our understanding of virtual environments. To do this, it examines in each case how the virtual reality systems are integrated into the curriculum, how these systems relate to the learning process, the usability of the systems, and the possibilities and constraints of the virtual worlds. By comparing these with other emerging virtual reality applications, such as entertainment games, it can be seen that different systems present a variety of possibilities for constructing presence in, and interaction with, virtual environments.     

What are virtual environments?

Virtual environment displays arose from vehicle simulation and teleoperations technology of the 1960s. They are interactive, head-referenced computer displays that give users the illusion of displacement to another location. Different terms have been applied to the illusion. Some, like the oxymoronic “artificial reality” and “virtual reality”, suggest much higher performance than current technology can generally provide. Others, like “cyberspace” are puzzling neologisms. Expressions like “virtual worlds” and “virtual environment” seem preferable because they are linguistically conservative, relating to well-established terms like virtual image. In fact, we can define virtual environments as interactive, virtual image displays enhanced by special processing and by nonvisual display modalities, such as auditory and haptic, to convince users that they are immersed in a synthetic space. Why are these displays useful? Who uses them? How are they developed? The article addresses these and other questions related to this emerging technology     

A poetry performance in a collaborative virtual environment

The article presents the design of a poetry performance in a collaborative virtual environment (CVE) and discusses the experience of staging this performance to an audience of 200 members of the general public. The performance involved an extensive collaboration among computer scientists, poets, a graphic artist, and an event production team. The article explores a range of technical and production issues arising from this experience, including: developing rich and engaging forms of content for CVEs; exploring the tension between autonomy of action for audience members and the management of a performance to encourage appropriate behaviors at relevant times and places; considering spatial scoping techniques in enabling different modes of awareness and communication between participants as an event unfolds; developing appropriate embodiments for performers and audience; developing appropriate navigation interfaces for different participants who may or may not have experienced virtual reality (VR); exploring different ways of situating interfaces to a virtual environment within different physical environments based on notions of mixed reality; understanding the issues involved in designing and managing such an event and how these might influence construction tools for CVEs