Backward Recovery Research Articles

Recovery from an unexpected standing-slip in professional ballet dancers

Although interventional studies have suggested that dance-based training may reduce fall risk for older adults based on unperturbed assessments, it remains unknown whether dance (particularly ballet) enhances recovery from an external perturbation. This preliminary study sought to test if and how ballet dancers respond differently to a novel standing-slip perturbation relative to non-dancers. Ten young professional ballet dancers and 10 age/sex-matched non-dancers were exposed to an unannounced slip while standing on the treadmill. Their reactions to the slip, characterized by dynamic gait stability (primary outcome), and the recovery stepping and trunk movements (secondary outcomes), were compared between groups. No significant group difference in dynamic gait stability was found at slip onset and recovery step liftoff, but dancers were more stable than non-dancers at touchdown (p = 0.046). Compared to non-dancers, dancers took a longer (p = 0.049) and faster (p = 0.007) backward recovery step and exhibited a less backward leaned trunk at all instants (p ≤ 0.026). Our study suggests that professional ballet dancers are more stable after a novel standing-slip than non-dancers. This better slip-related fall resistance among dancers could result from their more effective recovery stepping strategy and better trunk movement control after the slip. Both reactions may be attributed to ballet training, which requires frequent backward stepping and an upright trunk. Our findings could potentially provide preliminary evidence for applying ballet training to reduce balance losses and falls in people at a high fall risk. More studies are needed to examine ballet training’s effects among other populations with elevated fall risk in real-life situations.

Stabilized leapfrog scheme run backward in time, and the explicit O(Δ t)2 stepwise computation of ill-posed time-reversed 2D Navier–Stokes equations

Richardson's leapfrog scheme is notoriously unconditionally unstable in well-posed, forward, linear dissipative evolution equations. Remarkably, that scheme can be stabilized, marched backward in time, and provide useful reconstructions in an interesting but limited class of ill-posed, time-reversed, 2D incompressible Navier–Stokes initial value problems. Stability is achieved by applying a compensating smoothing operator at each time step to quench the instability. Eventually, this leads to a distortion away from the true solution. This is the stabilization penalty. In many interesting cases, that penalty is sufficiently small to allow for useful results. Effective smoothing operators based on , with real p>2, can be efficiently synthesized using FFT algorithms. Similar stabilizing techniques were successfully applied in several other ill-posed evolution equations. The analysis of numerical stability is restricted to a related linear problem. However, as is found in leapfrog computations of well-posed meteorological and oceanic wave propagation problems, such linear stability is necessary but not sufficient in the presence of nonlinearities. Here, likewise, additional Robert–Asselin–Williams (RAW) time-domain filtering must be used to prevent characteristic leapfrog nonlinear instability unrelated to ill-posedness. Several 2D Navier–Stokes backward reconstruction examples are included, based on the stream function-vorticity formulation, and focusing on pixel images of recognizable objects. Such images, associated with non-smooth underlying intensity data, are used to create severely distorted data at time T>0. Successful backward recovery is shown to be possible at parameter values significantly exceeding expectations.

Fault Tolerance Framework for Composite Web Services

A composite Web service combines multiple, logically interrelated services for creating more common services meeting complex requirements from users. The services participating in a composition coordinate the actions of distributed activity using Web services protocols to reach consistent agreement on the outcome of joint operation. However, as services run over unreliable protocols, there is a great chance that services fail due to the failure of protocols. However, current protocol standards provide fault-tolerance but are limited to backward recovery using expensive compensation and roll-back strategies. This paper gives an extension of the existing Web services business activity (WS-BA) protocol to deal with failures using forward recovery approach. A set of common failure types affecting the execution of component services is identified, and recovery solutions for each identified failure are also presented. The fault-handling extension of the WS-BA protocol implements recovery solutions for each of the identified failures to handle failures at runtime. Another important aspect about which the WS-BA protocol specification is unclear is reaching and notifying consistent outcome on the completion of joint work. This study extends the WS-BA protocol to notify consistent outcome reached by all participating services. The implementation and testing of the framework are performed using the model-checking and verification tool UPPAAL. A well-known application example supports the study. The key properties of the framework, like the execution of corresponding recovery actions in cases of failures and reaching a consistent agreement on the outcome of joint operation, are verified.

Safety Enhancement for Real-Time Parallel Applications in Distributed Automotive Embedded Systems: A Stable Stopping Approach

In distributed automotive embedded systems, safety issues run through the entire life cycle, and safety mechanisms for error handling are desirable for risk control. This article focuses on safety enhancement (i.e., safety mechanisms for error handling) for a safety-critical automotive application within its deadline. A stable stopping approach used for safety enhancement for an automotive application is proposed based on the static recovery mechanism provided in ISO 26262. The Stable Stopping-based Safety Enhancement (SSSE) approach is proposed by combining known backward recovery, proposed forward recovery, and proposed forward-and-backward recovery through primary-backup repetition. The stable stopping (i.e., SSSE) approach is a convergence algorithm, which means that when the reliability value reaches a steady state and the algorithm can stop. Experimental results reveal that the exposure level defined in ISO 26262 drops from E3 to E1 after using SSSE, and such improvement enables a safety guarantee of higher level.

Computing ill-posed time-reversed 2D Navier–Stokes equations, using a stabilized explicit finite difference scheme marching backward in time

This paper constructs an unconditionally stable explicit finite difference scheme, marching backward in time, that can solve an interesting but limited class of ill-posed, time-reversed, 2D incompressible Navier–Stokes initial value problems. Stability is achieved by applying a compensating smoothing operator at each time step to quench the instability. This leads to a distortion away from the true solution. However, in many interesting cases, the cumulative error is sufficiently small to allow for useful results. Effective smoothing operators based on , with real p>2, can be efficiently synthesized using FFT algorithms. Similar stabilizing techniques were successfully applied in other ill-posed evolution equations. The analysis of numerical stability is restricted to a related linear problem. However, extensive numerical experiments indicate that such linear stability results remain valid when the explicit scheme is applied to a significant class of time-reversed nonlinear 2D Navier–Stokes initial value problems. Several reconstruction examples are included, based on the stream function-vorticity formulation, and focusing on pixel images of recognizable objects. Such images, associated with non-smooth underlying intensity data, are used to create severely distorted data at time T>0. Successful backward recovery is shown to be possible at parameter values exceeding expectations.

Dependable composition of transactional web services using fault‐tolerance patterns and service scheduling

Building composite value-added services by combining basic services has become a prevalent way of software development. To provide the dependability in a composite service it is essential to combine the backward and forward recovery strategies properly based on composition level quality of service (QoS) factors or user preferences. The backward recovery, known as a fault-tolerance (FT) technique, is performed by compensating the successfully terminated services dependent on the failed service which may entail rollback costs. The forward recovery is achieved by applying FT patterns to each workflow task to decrease its failure rate. It has the disadvantages of longer invocation time and cost. Obviously the success of these methods in finding transactional compositions is highly dependent on the compensateability and retriability of services. In this study, four composition-level QoS factors have been defined to select between the forward or backward recovery strategies in the workflow. The problem of creating a dependable composite service is formulated as a multiobjective optimisation algorithm which explores not only the huge search space of different recovery strategies but also the cross-cutting search space of task scheduling. The effect of task scheduling on finding solutions with lower costs has been verified using case studies.

Failover strategy for fault tolerance in cloud computing environment

SummaryCloud fault tolerance is an important issue in cloud computing platforms and applications. In the event of an unexpected system failure or malfunction, a robust fault‐tolerant design may allow the cloud to continue functioning correctly possibly at a reduced level instead of failing completely. To ensure high availability of critical cloud services, the application execution, and hardware performance, various fault‐tolerant techniques exist for building self‐autonomous cloud systems. In comparison with current approaches, this paper proposes a more robust and reliable architecture using optimal checkpointing strategy to ensure high system availability and reduced system task service finish time. Using pass rates and virtualized mechanisms, the proposed smart failover strategy (SFS) scheme uses components such as cloud fault manager, cloud controller, cloud load balancer, and a selection mechanism, providing fault tolerance via redundancy, optimized selection, and checkpointing. In our approach, the cloud fault manager repairs faults generated before the task time deadline is reached, blocking unrecoverable faulty nodes as well as their virtual nodes. This scheme is also able to remove temporary software faults from recoverable faulty nodes, thereby making them available for future request. We argue that the proposed SFS algorithm makes the system highly fault tolerant by considering forward and backward recovery using diverse software tools. Compared with existing approaches, preliminary experiment of the SFS algorithm indicates an increase in pass rates and a consequent decrease in failure rates, showing an overall good performance in task allocations. We present these results using experimental validation tools with comparison with other techniques, laying a foundation for a fully fault‐tolerant infrastructure as a service cloud environment. Copyright © 2017 John Wiley & Sons, Ltd.

Enabling Support of Collaborative Cross-enterprise Business Processes for Legacy ERP Systems.

In order to create innovative business products, share knowledge between people and businesses, or increase the control and quality of services, more and more often enterprise business processes involve in collaborations by delegating or providing some pieces of work to other enterprises. Necessity to cooperate in the cross-enterprise setting leads to Collaborative Business Processes (CBPs). The difference between CBPs and Business Processes (BPs) is in the decentralized coordination, flexible backward recovery, participants notification about the state, efficient adaptability to changes, presence of multiple information systems, and individual authorization settings. In the paper we consider a specific case of CBPs where multiple collaborating partners use Enterprise Resource Planning (ERP) system of the same vendor. The vendor can see (e.g., monitor) the changes of data elements, but does not have explicit process awareness in the ERP system to support flow of activities in the cross-enterprise setting. The paper also discusses different settings of cross-enterprise CBP and shows simplified enterprise models behind the vendor possibilities to positively impact collaborative processes. The restrictions of the vendor are implicit information flows in BP, diversity of ERP integrations with third party Information Systems (IS), the lack of mechanisms for monitoring BP instances, backward recovery, user notification about the current state and tasks, and inability to make explicit changes in customers’ ISs.

Formal Specification of the Assurance Point Web Service Composition Model

This paper presents a formal specification of the Assurance Point (AP) web service composition model. The AP model provides a flexible way of checking constraints and responding to execution errors in service composition. An AP is a combined logical and physical checkpoint, providing an execution milestone that stores critical data and interacts with integration rules (IRs) to alter program flow and to invoke different forms of recovery depending on the execution status. In this paper, the execution and recovery semantics of assurance points have been fully defined in the context of if-else, parallel, and loop control structures. The activities and complex control structures of the AP model have been formalized and tested in the Yet Another Workflow Language (YAWL) engine. By doing so, the correctness of the execution and recovery semantics in the AP model has been verified, demonstrating that YAWL nets of the AP model satisfy the soundness property. Different from existing web service composition models, the AP model presented by this research provides multiple levels of protection against service execution failure with a combination of forward and backward recovery techniques.

Tx-FAITH

A key challenge in B2B and B2C applications involving dynamic composition of workflow activities is to ensure their reliable execution, in view of frequent failures in the internet environment where a composed service is executed. Existing approaches for transactional coordination of composite web services, consider forward and backward recovery alone, in order to maintain consistency in the case of failures. However, while achieving reliable execution, service cancellability is important due to the predominance of long running processes in business applications and frequently changing user requirements and business policies. If the execution of a long running process is not cancelled in the case of a changed requirement, the completion of the process results in wastage of resources and the outcome may no longer be useful. Hence, a transactional coordination framework named as Tx-FAITH is proposed to handle the cancellation recovery under the external interruption and cancellation of transactions. Tx-FAITH considers hierarchically composed web services whose components are recursively nested to form a composition and adapts a coordination approach based on context information. The proposed coordination and recovery approach when tested with 200 simultaneous users and with a database size of 0.35 million records, incurs only 10 seconds to process a request.

RDTA

Web services are very dynamic, they are all around us and we use them every day without even knowing it. In this paper, the authors define a formal model for dynamic Web services composition and they investigate how it can be used to specify and analyse backward recovery procedures, updating partner services in case of failure. First, they propose Recursive and Dynamic Timed Automata (RDTA) model, interpreted over composite service configurations, which provide a natural way to design stateful and dynamic Web services. Then, the authors define the concurrent semantics of this timed automata extension in terms of real-time rewrite theories. Analysis of the model is carried out in the Real-Time Maude system, based on checking relevant properties.

A new method of extraction of amoxicillin using mixed reverse micelles

A completely new method of extraction of amoxicillin using solubilisation by mixed reverse micelles was proposed and the optimal conditions for the process were found. Mixed AOT-TWEEN 85 reverse micelles were used for the first time as a new approach for extraction of amoxicillin. The effects of different process variables such as AOT-TWEEN 85 molar fractions, total surfactant concentration, pH of aqueous feed solution and potassium chloride concentration during forward extraction; stripping aqueous phase pH, potassium chloride (KCl) concentration and extraction time during backward extraction were investigated and the optimal conditions were found for all mentioned parameters. With the aid of response surface methodology, the optimum conditions for forward extraction are identified as (i) 5.5:1 molar ratio of AOT/TWEEN 85, (ii) total surfactant concentration 102.57g/L, (ii) pH 1.90, and (vi) KCl concentration 8.54g/L. The percentage of amoxicillin solubilised in isooctane was 95.54% under these optimal conditions. On the other hand, the optimum conditions for backward extraction are identified as (i) stripping aqueous phase pH 6.58, (ii) KCl concentration 11.02g/L, and (iii) extraction time 15min. Under these optimal conditions, the percentage of amoxicillin recovered was 90.79%. AOT/TWEEN 85 mixed surfactant system shows a significant advantage of saving the amount of surfactant for forward extraction. The addition of non-ionic surfactant helps to preserve natural function/activity of antibiotics as compared with a pure AOT surfactant used. The optimum conditions were also found for a backward recovery of amoxicillin.

Extraction of tea polysaccharides (TPS) using anionic reverse micellar system

Reverse micelles extraction technology are efficient and economical alternative for extraction of bioactive molecules due to its high selectivity, fast mass transfer and relatively low cost. In this study, AOT can form wide range of reverse micellar core sizes in organic phase, which has been used to extract tea polysaccharides (TPS) in AOT/heptane reverse micellar system. Process conditions were optimized by pH, types and concentration of salts, types and concentration of alcohols. Chaotropes (GuHCl and urea) were used to improve extraction yield of tea polysaccharides in the system. In forward extraction, low concentration of GuHCl in this AOT/heptane system may influence the TPS structure and suppress its aggregation formation and promote its solubilization into the water cores. Under optimal conditions (pH 4.6, 0.05molL−1 NaCl, 7% [v/v] methanol and 0.06molL−1 GuHCl), the forward extraction recovery reached 34%. In backward extraction, 100% of backward recovery was achieved by adding GuHCl or urea.

A Comprehensive Failure Recovery Algorithm for LRTs Based on Paired Net

Failure recovery optimization is an important way for enhancing efficiency of Long Running Transaction (LRT) processing. In this paper, to solve the efficiency problem of LRT failure recovery, a Comprehensive Recovery Model for LRTs (LCRM) is constructed, which divides LRTs into a series of sub-transactions in different levels, and supports versatile transaction properties of LRT. Based on LCRM, a Comprehensive Failure Recovery algorithm for LRTs (LCFR) is proposed. This algorithm uses methods of forward recovery, backward recovery and alternative recovery. It supports auto-recovery of failures during the execution of LRTs. LCFR guarantees LRT’s semantic atomicity property and durability property. By restricting the recovery scope in lower level of complex LRTs, LCFR limits the quantity of sub-transactions to be recovered. Thus, it reduces unnecessary loss of time and enhances the efficiency of failure recovery. Experiment results show that LCFR can reduce the time required for failure recovery and decrease the failure rate of LRT processing.

FACETA*: Checkpointing for Transactional Composite Web Service Execution based on Petri-Nets

Failures during the execution of Transactional Composite Web Services (TCWSs) can be repaired by forward or back–ward recovery processes, according to the component WSs transactional properties. In previous works, we presented TCWS fault tolerant execution approaches relying on WSs replacement, on a compensation protocol, and on unrolling processes of Colored Petri-Nets (CPNs) to support forward and backward recovery. We represent a TCWS and its corresponding backward recovery process by CPNs. Even though these recovery processes ensure system consistency, backward recovery means that users do not get the desired answer to their queries and forward recovery could imply long waiting time for users to finally get the desired response. In this paper, we present an alternative fault tolerant approach in which, in case of failures, the unrolling process of the CPN controlling the execution of a TCWS is check–pointed and the execution flow goes on as much as it is possible. In this way, users can have partial responses as soon as they are received and can re-submit the checkpointed CPN to re-start its execution from an advanced point of execution (checkpoint). We present the checkpointing algorithm integrated to our previous work.

A Backward Recovery Mechanism in Preemptive Utility Accrual Real Time Scheduling Algorithm

Problem statement: This study proposed a robust algorithm named as Backward Recovery Preemptive Utility Accrual Scheduling (BRPUAS) algorithm that implements the Backward Recovery (BR) mechanism as a fault recovery solution under the existing utility accrual scheduling environment. The problem identified in the TUF/UA scheduling domain is that the existing algorithms only considers the Abortion Recovery (AR) as their fault recovery solution in which all faulty tasks are simply aborted to nullify the erroneous effect. The decision to immediately abort the affected tasks is inefficient because aborted tasks produce zero utility causes the system to accrue lower utility. Approach: The proposed BRPUAS algorithm enabled the re-execution of the affected tasks rather than abortion to reduce the number of aborted task in the existing algorithm known as Abortion Recovery Preemptive Utility Accrual Scheduling (ARPUAS) algorithm that employed the AR mechanism. The BRPUAS ensure the correctness of the executed tasks in the best effort basis in such a way that the infeasible tasks are aborted and produced zero utility, while the feasible tasks are re-executed to produce positive utility and consequently maximized the total accrued utility to the system. The performances of these algorithms are measured by using discrete event simulation. Results: The proposed BRPUAS algorithm achieved higher accrued utility compared to ARPUAS for the entire load range. Conclusion: Simulation results revealed that the BR mechanism is more efficient than the existing AR mechanism, producing higher accrued utility ratio and less abortion ratio making it more reliable and efficient for adaptive real time application domain.

Fault Recovery Mechanisms in Utility Accrual Real Time Scheduling Algorithm

In this paper, we proposed two recovery solutions over the existing error-free utility accrual scheduling algorithm known as General Utility Accrual Scheduling algorithm (or GUS) (Peng Li, 2004). A robust fault recovery algorithm called Backward Recovery GUS (or BRGUS) works by adapting the time redundancy model i.e., by re-executing the affected task after its transient error period is over. The BRGUS is compared with a less complicated recovery algorithm named as Abortion Recovery GUS (or ARGUS) that simply aborts all faulty tasks. Our main objectives are (1) to maximize the total accrued utility and (2) to ensure correctness of the executed tasks on best effort basis and achieve the fault free tasks as much as possible. Our simulation results reveal that BRGUS outperforms the ARGUS algorithm with higher accrued utility and less abortion ratio, making it more suitable and efficient in adaptive real time system.

Towards flexible compensation for business transactions in Web service environment

Recently, many business applications embrace Web services as their implementation technologies. Due to the long duration and loosely coupled properties, Web service based applications require more transactional supports beyond traditional transactions. Some initial work has been done to deal with the transaction aspect of Web service applications, in form of standards or protocols. Among these efforts, compensation is commonly used for backward recovery. However, the compensation mechanism adopted is too fixed and cannot satisfy the various requirements of different applications. In this paper, we propose a flexible compensation mechanism which enables flexible compensation schemes for a single failed case. Based on a thorough analysis of current Web service compensation protocols and standards, we extend the flexible compensation mechanism to the Web service computing environment. The implementation of the extended compensation mechanism is discussed and the incorporation of the mechanism into current standards is also addressed.

An environment for flexible advanced compensations of Web service transactions

Business to business integration has recently been performed by employing Web service environments. Moreover, such environments are being provided by major players on the technology markets. Those environments are based on open specifications for transaction coordination. When a failure in such an environment occurs, a compensation can be initiated to recover from the failure. However, current environments have only limited capabilities for compensations, and are usually based on backward recovery. In this article, we introduce an environment to deal with advanced compensations based on forward recovery principles. We extend the existing Web service transaction coordination architecture and infrastructure in order to support flexible compensation operations. We use a contract-based approach, which allows the specification of permitted compensations at runtime. We introduce abstract service and adapter components, which allow us to separate the compensation logic from the coordination logic. In this way, we can easily plug in or plug out different compensation strategies based on a specification language defined on top of basic compensation activities and complex compensation types. Experiments with our approach and environment show that such an approach to compensation is feasible and beneficial. Additionally, we introduce a cost-benefit model to evaluate the proposed environment based on net value analysis. The evaluation shows in which circumstances the environment is economical.

FENECIA: failure endurable nested-transaction based execution of composite Web services with incorporated state analysis

Interest in the Web services (WS) composition (WSC) paradigm is increasing tremendously. A real shift in distributed computing history is expected to occur when the dream of implementing Service-Oriented Architecture (SOA) is realized. However, there is a long way to go to achieve such an ambitious goal. In this paper, we support the idea that, when challenging the WSC issue, the earlier that the inevitability of failures is recognized and proper failure-handling mechanisms are defined, from the very early stage of the composite WS (CWS) specification, the greater are the chances of achieving a significant gain in dependability. To formalize this vision, we present the FENECIA (Failure Endurable Nested-transaction based Execution of Composite Web services with Incorporated state Analysis) framework. Our framework approaches the WSC issue from different points of view to guarantee a high level of dependability. In particular, it aims at being simultaneously a failure-handling-devoted CWS specification, execution, and quality of service (QoS) assessment approach. In the first section of our framework, we focus on answering the need for a specification model tailored for the WS architecture. To this end, we introduce WS-SAGAS, a new transaction model. WS-SAGAS introduces key concepts that are not part of the WS architecture pillars, namely, arbitrary nesting, state, vitality degree, and compensation, to specify failure-endurable CWS as a hierarchy of recursively nested transactions. In addition, to define the CWS execution semantics, without suffering from the hindrance of an XML-based notation, we describe a textual notation that describes a WSC in terms of definition rules, composability rules, and ordering rules, and we introduce graphical and formal notations. These rules provide the solid foundation needed to formulate the execution semantics of a CWS in terms of execution correctness verification dependencies. To ensure dependable execution of the CWS, we present in the second section of FENECIA our architecture THROWS, in which the execution control of the resulting CWS is distributed among engines, discovered dynamically, that communicate in a peer-to-peer fashion. A dependable execution is guaranteed in THROWS by keeping track of the execution progress of a CWS and by enforcing forward and backward recovery. We concentrate in the third section of our approach on showing how the failure consideration is trivial in acquiring more accurate CWS QoS estimations. We propose a model that assesses several QoS properties of CWS, which are specified as WS-SAGAS transactions and executed in THROWS. We validate our proposal and show its feasibility and broad applicability by describing an implemented prototype and a case study.