Gryphon: An Information Flow Based Approach to Message Brokering

Gryphon is a distributed computing paradigm for message brokering, which is the transferring of information in the form of streams of events from information providers to information consumers. This extended abstract outlines the major problems in message brokering and Gryphon's approach to solving them.Comment: Two page extended abstrac

MSF-Model: Modeling Metastable Failures in Replicated Storage Systems

Metastable failure is a recent abstraction of a pattern of failures that occurs frequently in real-world distributed storage systems. In this paper, we propose a formal analysis and modeling of metastable failures in replicated storage systems. We focus on a foundational problem in distributed systems -- the problem of consensus -- to have an impact on a large class of systems. Our main contribution is the development of a queuing-based analytical model, MSF-Model, that can be used to characterize and predict metastable failures. MSF-Model integrates novel modeling concepts that allow modeling metastable failures which was interactable to model prior to our work. We also perform real experiments to reproduce and validate our model. Our real experiments show that MSF-Model predicts metastable failures with high accuracy by comparing the real experiment with the predictions from the queuing-based model

Cognitive load and the role of cue utilisation during sustained attention tasks

Theoretical thesis.Bibliography: pages 267-301.Chapter 1. Introduction -- Chapter 2, Cue Utilisation -- Chapter 3. Overview of research questions -- (Study 1&2, 3,4,5,6) -- General discussion.One of the key roles of system controllers in high risk environments, such as rail control, power control, and driving, is to recognise, anticipate and respond to changes in the system state. This requires that operators sustain a visual search to monitor and control their operating systems, often for extended periods. However, attentional resource theory posits that sustaining attention over extended periods results in the consumption of cognitive resources, thereby reducing the residual resources available to manage changes in the system state. The utilisation of cues is a cognitive strategy that operators engage to reduce the rate at which cognitive resources are consumed. The aim of this thesis was to examine whether differences in cue utilisation are associated with differences in the rate at which cognitive resources are consumed across a range of operational settings, under a range of operational conditions, and using operators of varying levels of operator experience. Studies 1 and 2 w ere conducted to establish whether a general capacity for cue utilisation predicts differences in the consumption of cognitive resources during sustained attention tasks. The results of Study 1 indicated that participants with higher cue utilisation recorded smaller increases in mean response latency during a novel 30 - minute rail control simulation, compared to participants with lower cue utilisation . Study 2 replicated and extended these results using a 45 - minute rail control simulation, demonstrating greater decreases in fixation rates, smaller changes in cerebral oxygenation in the prefrontal cortex, and smaller increases in mean response latency for participants with higher cue utilisation, compared to participants with lower cue utilisation. These results are consistent with the proposition that cue utilisation is associated with the allocation of fewer cognitive resources to sustained attention task.Study 3 was designed to validate a newly adapted sustained visual search task for process control environments. The results revealed changes in response latency throughout the sustained visual search task that were positively associated with changes in response latency 12 during a 30 - minute low signal probability rail control task, a 45 - minute low signal probability rail control task, and a 45 - minute high signal probability rail control task. The findings suggest that the sustained visual search task is a valid alternative to a longer - duration process control task for experimental studies. Study 4 was intended to examine whether experienced operators' cue utilisation differentiates performance during domain - relevant sustained attention tasks. In two experiments, power distribution operators with higher cue utilisation demonstrated shorter mean response latencies during a power control sustained visual search task, compared to operators with lower cue utilisation . These results support the view that experienced operators with higher cue utilisation adopt strategies during operational tasks that reduce the demands on cognitive load. Study 5 was designed to establish whether differences in cognitive load based o n cue utilisation are also evident in more dynamic operational environments. Using motor vehicle driving as a context, drivers' consumption of cognitive resources were examined during a 20 - minute , simulated driving task. Qualified drivers with higher cue utilisation demonstrated smaller mean visual saccade amplitudes, smaller mean fixation dispersions, smaller increases in cerebral oxygenation and recorded fewer missed traffic signals during the simulated driving task, com pared to participants with lower cue utilisation . These results are consistent with the broader proposition that experienced operators adopt more efficient search patterns, and consume fewer cognitive resources, during dynamic operational task.Extending these findings, Study 6 assessed physiological measures of cognitive resource consumption during periods of power distribution operators' regular workdays. Across two testing sessions, and controlling for subjective measures of workload, higher cue utilisation was associated with smaller increases in cerebral oxygenation in the prefrontal cortex, which is indicative of lower cognitive load. These results indicate that experience operators with higher cue utilisation are consuming fewer cognitive resources during typical operational tasks, compared to operators with lower cue utilisation. The outcomes from this programme of research provide a number of theoretical contributions that advance an understanding of the relationship between cue utilisation and sustained attention. These contributions include support for the proposition that cue utilisation is associated with the consumption of fewer cognitive resources during sustained attention tasks, the identification of search pattern efficiency as a potential mediator for the relationship between cue utilisation and cognitive load, and evidence to support the resource depletion theory of the vigilance decrement. These findings have applied implications for the selection, management, and training of operators in high risk environments.1 online resource (308 pages

A Simulator for Exploring Replication and Locality of Access in a Distributed Database

In fault-tolerant distributed databases, one method of increasing data availability is through increased data replication. However, with increased data replication comes an increase in the time to perform transactions. What is needed is a way in which this and other problems involved with configuring distributed databases can be explored. This paper describes a simulator which provides an accurate model of many different distributed environments when given a set of parameters describing failures, data replication, and site organization. Such a simulator is a useful tool for exploring the behavior of possible distributed database configurations as well as for verifying theoretical results

What are the educational affordances of wearable technologies?

By providing users with hands-free access to contextually relevant knowledge, wearable technologies are poised to inspire a new generation of mobile learning design. However, in order for educators to harness the pedagogical opportunities of wearable technologies it is crucial for them to develop an understanding of their potentials, or 'affordances'. This paper analysed the perceptions of 66 educators from around the world who self-rated as having a 'good' or 'very good' understanding of wearable technologies to determine the key educational affordances and issues at stake. Qualitative thematic analysis of participant perceptions, as well as relevant literature, revealed fourteen affordances of wearable technologies and thirteen issues relating to their use. These clustered together into three emergent themes; 'pedagogical uses', 'educational quality' and 'logistical'. Utilising the insights of knowledgeable practitioners resulted in nine affordances and issues not identified in the literature, and within the literature there were three issues not identified by the knowledgeable practitioners. The implications of findings for the future of wearable technology learning design are also discussed.11 page(s

MODULAR SPECIFICATION OF INTERACTION POLICIES IN DISTRIBUTED COMPUTING

Software executing on distributed systems consists of many asynchronous, autonomous components which interact in order to coordinate local activity. The need for such coordination, as well as requirements such as heterogeneity, scalability, security and availability, considerably increase the complexity of code in distributed applications. Moreover, changing requirements, as well as changes in hardware platforms, lead to software that is constantly evolving and complicates reuse. To support development and evolution of distributed applications requires techniques which allow coordination code to be specified, customized, and maintained independently of application components; goals which cannot be realized solely through object-oriented techniques. This thesis demonstrates that meta-level specification of interaction policies enables modular description of component interaction policies, as well as customization of policy implementations. We present the high-level language Dil for specification of protocols. The language identifies the abstractions and concepts required for modular specification of interaction policies. The abstractions developed in Dil are then realized through a meta-level architecture. We provide several Dil protocols implementing policies for reliable communication, atomicity, and dependability in a multi-media application. The implementation techniques necessary to realize the meta-architecture are discussed in the context of Broadway, a run-time system for distributed C++ objects. This meta-architecture provides access to the system-level features necessary to support the modularity mechanisms defined in Dil. We provided examples of protocol translation from Dil to Broadway C++ classes that utilize the meta-architecture. Measurements show that these techniques may be implemented with minimal performance overhead. A formal semantics for reasoning about the approach is also developed

Modular specification of interaction policies in distributed computing

Software executing on distributed systems consists of many asynchronous, autonomous components which interact in order to coordinate local activity. The need for such coordination, as well as requirements such as heterogeneity, scalability, security and availability, considerably increase the complexity of code in distributed applications. Moreover, changing requirements, as well as changes in hardware platforms, lead to software that is constantly evolving and complicates reuse. To support development and evolution of distributed applications requires techniques which allow coordination code to be specified, customized, and maintained independently of application components; goals which cannot be realized solely through object-oriented techniques.This thesis demonstrates that meta-level specification of interaction policies enables modular description of component interaction policies, as well as customization of policy implementations. We present the high-level language D scIL for specification of protocols. The language identifies the abstractions and concepts required for modular specification of interaction policies. The abstractions developed in D scIL are then realized through a meta-level architecture. We provide several D scIL protocols implementing policies for reliable communication, atomicity, and dependability in a multi-media application.The implementation techniques necessary to realize the meta-architecture are discussed in the context of Broadway, a run-time system for distributed C++ objects. This meta-architecture provides access to the system-level features necessary to support the modularity mechanisms defined in D scIL. We provided examples of protocol translation from D scIL to Broadway C++ classes that utilize the meta-architecture. Measurements show that these techniques may be implemented with minimal performance overhead. A formal semantics for reasoning about the approach is also developed.U of I OnlyETDs are only available to UIUC Users without author permissio