Data replication is a key building block for large-scale distributed systems to improve availability, performance, and scalability. Because there is a fundamental trade-off between performance and consistency as well as between availability and consistency, systems must make trade-offs among these factors based on the demands and technologies of their target environments and workloads. Unfortunately, existing replication protocols and mechanisms are intrinsically entangled with specific policy assumptions. Therefore, to accommodate new trade-offs for new policy requirements, developers have to either build a new replication system from scratch or modify existing mechanisms. This dissertation presents a universal data replication architecture (URA) that cleanly separates mechanism and policy and supports Partial Replication (PR), Any Consistency (AC), and Topology Independence (TI) simultaneously. Our architecture yields two significant advantages. First, by providing a single set of mechanisms that capture the common underlying abstractions for data replication, URA can serve as a common substrate for building and deploying new replication systems. It therefore can significantly reduce the effort required to construct or modify a replication system. Second, by providing a set of general and flexible mechanisms independent of any specific policy, URA enables better trade-offs than any current system can provide. In particular, URA can simultaneously provide the three PRACTI properties while any existing system can provide at most two of them. Our experimental results and case-study systems confirm that universal data replication architecture is a way to build better replication systems and a better way to build replication systems. / text

OurFileSystem (OFS) is a peer-to-peer file and metadata sharing program. Peers freely join the network, but must be granted access to groups in which metadata and files are shared. Any peer may create a group and grant others access to the group. Group members have different degrees of authority to grant others access and set their authority. Metadata for files is created by users within the context of a group and distributed to all members of the group in the form of a post. Post templates can be created to set fields of metadata. Templates are distributed to all members of a group, and one can be selected when creating a post or searching for files. Metadata in posts is indexed, and sophisticated search on the metadata can be performed locally to help users find files of interest quickly. Files found during a search may be downloaded from peers upon request. Pieces of files are downloaded from as many different peers as possible to maximize bandwidth. Peers within a group may also be marked as bad locally. If a user marks another peer as bad within the context of a group, posts from that peer to the group are deleted and not shared with others. Furthermore, any peer that was granted access by a peer marked as bad is also marked bad. No further posts or authorizations are ever accepted from any peer marked as bad. OFS also supports small public and private messages, which are distributed to all peers in the network. Private messages are encrypted so only the intended peer can decrypt the message. Lastly OFS integrates well with anonymous overlay networks that support SOCKS proxies, such as TOR. I2P support has also been explicitly added. / text

Abstractions are widely used in building reliable distributed systems as they simplifies the task of building complex systems and aid in reasoning about them. Implementing these abstractions, however, requires making certain assumptions about the environment in which they will be used. We find that there is a mismatch in the set of assumptions used to implement abstractions in the different layers of a distributed system. This leads to a costlier design and may render the implementation unusable in situations where the assumptions do not hold. In this dissertation we provide alternative implementations for the abstractions of distributed registers and communication channels that rely on a unified set of assumptions across the different layers of a distributed system. / text

This is a presentation of 21 slides at the Leadership Development session of the ASIST 2005 Annual Meeting at Charlotte, N.C. on October 30. It discusses the 2002 virtual community building experiment undertaken by the Arizona Chapter of ASIST. The chapter experimented with three different pieces of software, a wiki, a content management system, and slashcode. This presentation was also video-taped and may become available through the ASIST website, http://www.asis.org/.

From the Executive Summary of the 67 page Report: The National Science Board (NSB, the Board) recognizes the growing importance of these digital data collections for research and education, their potential for broadening participation in research at all levels, the ever increasing National Science Foundation (NSF, the Foundation) investment in creating and maintaining the collections, and the rapid multiplication of collections with a potential for decades of curation. In response the Board formed the Long-lived Data Collections Task Force. The Board and the task force undertook an analysis of the policy issues relevant to long-lived digital data collections. This report provides the findings and recommendations arising from that analysis. The primary purpose of this report is to frame the issues and to begin a broad discourse. Specifically, the NSB and NSF working together â with each fulfilling its respective responsibilities â need to take stock of the current NSF policies that lead to Foundation funding of a large number of data collections with an indeterminate lifetime and to ask what deliberate strategies will best serve the multiple research and education communities. The analysis of policy issues in Chapter IV and the specific recommendations in Chapter V of this report provide a framework within which that shared goal can be pursued over the coming months. The broader discourse would be better served by interaction, cooperation, and coordination among the relevant agencies and communities at the national and international levels. Chapters II and III of this report, describing the fundamental elements of data collections and curation, provide a useful reference upon which interagency and international discussions can be undertaken. The Board recommends that the Office of Science and Technology Policy (OSTP) take the lead in initiating and coordinating these interagency and international discussions.

Please use the following citation when referencing this material: Dillon and Gabbard (1998) Hypermedia as an educational technology: a review of the empirical literature on learner comprehension, control and style. Review of Educational Research, 68(3), 322, 349. Reprinted in P. Smith and A. Pellegrinni (eds.) (2000) The Psychology of Education: Major Themes, London: Routledge, 3, 496-531. Abstract: By virtue of its enabling rapid, non-linear access to multiple forms of information, hypermedia technology is considered a major advance in the development of educational tools to enhance learning and a massive literature on the use of hypermedia in education has emerged. The present review examines the published findings from experimental studies of hypermedia which emphasized quantitative, empirical methods to assess learning outcomes. Specifically, the review categorizes this research into three themes: studies of learner comprehension compared across hypermedia and other media; effects on learning outcome offered by increased learner control in hypermedia environments, and the individual differences that exist in learner response to hypermedia. The review concludes that to date, the benefits of hypermedia in education are limited to learning tasks reliant on repeated manipulation and searching of information, and are differentially distributed across learners depending on their ability and preferred learning style. Methodological and analytical shortcomings in this literature limit the generalizability of all findings in this domain. Suggestions for addressing these problems in future research and theory development are outlined.

Using Information Technology to Transform the Way We Learn highlights PITACâ s findings and recommendations on how the Federal government can provide the leadership needed to solve key information technology challenges and to improve the quality of, and public access to educational and training experiences. The overarching recommendation in this report calls for the Federal government to make the integration of information technology with education and training a national priority. In addition, the Federal government should: *Establish and coordinate a major research initiative for information technology in education and training *Establish focused government-industry-foundation partnerships to aggressively pursue the information technology research program *Develop programs that enable educators and related professionals to use information technology effectively *Work with industry and academia to develop technical standards for extendable component-based technologies and infrastructures that can be widely used in online education and training

Access to educational material has become an important issue for many stakeholders and the focus of many projects worldwide. Resource discovery in many educational gateways is usually based on metadata and this is the area of many important developments. Resource metadata has a central role in the management of educational material and as a result there are several important metadata standards in use in the educational domain. One of the most widely used general metadata standards for learning material is the Dublin Core Metadata Element Set. The application of this general purpose, metadata standard for complex and heterogeneous educational material is not straightforward. This paper will give an overview of some practical issues and necessary steps in deploying Dublin Core based on the LITC experience in EASEL (Educators Access to Services in the Electronic Landscape)project.

There is a serious lack of conceptual clarity in the definitions and uses of learning objects, resulting in design and usability problems in current e-learning systems. The paper proposes ReLOMS, prototype reusable learning objects management system, being implemented to address the problem of usability and reusability of learning objects in e-learning systems.

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