Wenbing Zhao

Fault Tolerance Middleware for Cloud Computing

The Low Latency Fault Tolerance (LLFT) middleware provides fault tolerance for distributed applications deployed within a cloud computing or data center environment, using the leader/follower replication approach. The LLFT middleware consists of a Low Latency Messaging Protocol, a Leader-Determined Membership Protocol, and a Virtual Determinizer Framework. The Messaging Protocol provides are liable, totally ordered message delivery service by employing a direct group-to-group multicast where the ordering is determined by the primary replica in the group. The Membership Protocol provides a fast reconfiguration and recovery service when a replica becomes faulty and when a replica joins or leaves a group. The Virtual Determinizer Framework captures ordering information at the primary replica and enforces the same ordering at the backup replicas for major sources of non-determinism. The LLFT middleware maintains strong replica consistency, offers application transparency, and achieves low end-to-end latency.

A Survey of Applications and Human Motion Recognition with Microsoft Kinect

Microsoft Kinect, a low-cost motion sensing device, enables users to interact with computers or game consoles naturally through gestures and spoken commands without any other peripheral equipment. As such, it has commanded intense interests in research and development on the Kinect technology. In this paper, we present, a comprehensive survey on Kinect applications, and the latest research and development on motion recognition using data captured by the Kinect sensor. On the applications front, we review the applications of the Kinect technology in a variety of areas, including healthcare, education and performing arts, robotics, sign language recognition, retail services, workplace safety training, as well as 3D reconstructions. On the technology front, we provide an overview of the main features of both versions of the Kinect sensor together with the depth sensing technologies used, and review literatures on human motion recognition techniques used in Kinect applications. We provide a classification of motion recognition techniques to highlight the different approaches used in human motion recognition. Furthermore, we compile a list of publicly available Kinect datasets. These datasets are valuable resources for researchers to investigate better methods for human motion recognition and lower-level computer vision tasks such as segmentation, object detection and human pose estimation.

BFT-WS: A Byzantine Fault Tolerance Framework for Web Services

Many Web services are expected to run with high degree of security and dependability. To achieve this goal, it is essential to use a Web-services compatible framework that tolerates not only crash faults, but Byzantine faults as well, due to the untrusted communication environment in which the Web services operate. In this paper, we describe the design and implementation of such a framework, called BFT-WS. BFT-WS is designed to operate on top of the standard SOAP messaging framework for maximum interoperability. It is implemented as a pluggable module within the Axis2 architecture, as such, it requires minimum changes to the Web applications. The core fault tolerance mechanisms used in BFT-WS are based on the well-known Castro and Liskovs BFT algorithm for optimal efficiency. Our performance measurements confirm that BFT-WS incurs only moderate runtime overhead considering the complexity of the mechanisms.

Unification of transactions and replication in three-tier architectures based on CORBA

In this paper, we describe a software infrastructure that unifies transactions and replication in three-tier architectures and provides data consistency and high availability for enterprise applications. The infrastructure uses transactions based on the CORBA object transaction service to protect the application data in databases on stable storage, using a roll-backward recovery strategy, and replication based on the fault tolerant CORBA standard to protect the middle-tier servers, using a roll-forward recovery strategy. The infrastructure replicates the middle-tier servers to protect the application business logic processing. In addition, it replicates the transaction coordinator, which renders the two-phase commit protocol nonblocking and, thus, avoids potentially long service disruptions caused by failure of the coordinator. The infrastructure handles the interactions between the replicated middle-tier servers and the database servers through replicated gateways that prevent duplicate requests from reaching the database servers. It implements automatic client-side failover mechanisms, which guarantee that clients know the outcome of the requests that they have made, and retries aborted transactions automatically on behalf of the clients.

Trustworthy Coordination of Web Services Atomic Transactions

The Web Services Atomic Transactions (WS-AT) specification makes it possible for businesses to engage in standard distributed transaction processing over the Internet using Web Services technology. For such business applications, trustworthy coordination of WS-AT is crucial. In this paper, we explain how to render WS-AT coordination trustworthy by applying Byzantine Fault Tolerance (BFT) techniques. More specifically, we show how to protect the core services described in the WS-AT specification, namely, the Activation service, the Registration service, the Completion service and the Coordinator service, against Byzantine faults. The main contribution of this work is that it exploits the semantics of the WS-AT services to minimize the use of Byzantine Agreement (BA), instead of applying BFT techniques naively, which would be prohibitively expensive. We have incorporated our BFT protocols and mechanisms into an open-source framework that implements the WS-AT specification. The resulting BFT framework for WS-AT is useful for business applications that are based on WS-AT and that require a high degree of dependability, security, and trust.

A reservation-based coordination protocol for Web services

Traditional transaction semantics are not appropriate for business activities that involve long-running transactions in a loosely-coupled distributed environment, in particular, for Web services that operate between different enterprises over the Internet. In this paper we describe a novel reservation-based extended transaction protocol that can be used to coordinate such business activities. The protocol avoids the use of compensating transactions, which can result in undesirable effects. In our protocol, each task within a business activity is executed as two steps. The first step involves an explicit reservation of resources. The second step involves the confirmation or cancellation of the reservation. Each step is executed as a separate traditional short-running transaction. We show how our protocol can be implemented as a reservation protocol on top of the Web services transaction specification or, alternatively, as a coordination protocol on top of the Web services coordination specification.

Realtime Motion Assessment For Rehabilitation Exercises: Integration Of Kinematic Modeling With Fuzzy Inference

Abstract This article describes a novel approach to realtime motion assessment for rehabilitation exercises based on the integration of comprehensive kinematic modeling with fuzzy inference. To facilitate the assessment of all important aspects of a rehabilitation exercise, a kinematic model is developed to capture the essential requirements for static poses, dynamic movements, as well as the invariance that must be observed during an exercise. The kinematic model is expressed in terms of a set of kinematic rules. During the actual execution of a rehabilitation exercise, the similarity between the measured motion data and the model is computed in terms of their distances, which are then used as inputs to a fuzzy interference system to derive the overall quality of the execution. The integrated approach provides both a detailed categorical assessment of the overall execution of the exercise and the degree of adherence to individual kinematic rules.

A Kinect-based rehabilitation exercise monitoring and guidance system

In this paper, we describe the design and implementation of a Kinect-based system for rehabilitation exercises monitoring and guidance. We choose to use the Unity framework to implement our system because it enables us to use virtual reality techniques to demonstrate detailed movements to the patient, and to facilitate examination of the quality and quantity of the patient sessions by the clinician. The avatar-based rendering of motion also preserves the privacy of the patients, which is essential for healthcare systems. The key contribution of our research is a rule-based approach to realtime exercise quality assessment and feedback. We developed a set of basic rule elements that can be used to express the correctness rules for common rehabilitation exercises.

A feasibility study of using a single Kinect sensor for rehabilitation exercises monitoring: A rule based approach

In this paper, we present a feasibility study for using a single Microsoft Kinect sensor to assess the quality of rehabilitation exercises. Unlike competing studies that have focused on the validation of the accuracy of Kinect motion sensing data at the level of joint positions, joint angles, and displacement of joints, we take a rule based approach. The advantage of our approach is that it provides a concrete context for judging the feasibility of using a single Kinect sensor for rehabilitation exercise monitoring. Our study aims to answer the following question: if it is found that Kinects measurement on a metric deviates from the ground truth by some amount, is this an acceptable error? By defining a set of correctness rules for each exercise, the question will be answered definitively with no ambiguity. Defining appropriate context in a validation study is especially important because (1) the deviation of Kinect measurement from the ground truth varies significantly for different exercises, even for the same joint, and (2) different exercises have different tolerance levels for the movement restrictions of body segments. In this study, we also show that large but systematic deviations of the Kinect measurement from the ground truth are not as harmful as it seems because the problem can be overcome by adjusting parameters in the correctness rules.

Rule based realtime motion assessment for rehabilitation exercises

In this paper, we describe a rule based approach to realtime motion assessment of rehabilitation exercises. We use three types of rules to define each exercise: (1) dynamic rules, with each rule specifying a sequence of monotonic segments of the moving joint or body segment, (2) static rules for stationary joints or body segments, and (3) invariance rules that dictate the requirements of moving joints or body segments. A finite state machine based approach is used in dynamic rule specification and realtime assessment. In addition to the typical advantages of the rule based approach, such as realtime motion assessment with specific feedback, our approach has the following advantages: (1) increased reusability of the defined rules as well as the rule assessment engine facilitated by a set of generic rule elements; (2) increased customizability of the rules for each exercise enabled by the use of a set of generic rule elements and the use of extensible rule encoding method; and (3) increased robustness without relying on expensive statistical algorithms to tolerate motion sensing errors and subtle patient errors.