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Inverted Index Compression Using Word-Aligned Binary Codes   总被引:3,自引:1,他引:3  
We examine index representation techniques for document-based inverted files, and present a mechanism for compressing them using word-aligned binary codes. The new approach allows extremely fast decoding of inverted lists during query processing, while providing compression rates better than other high-throughput representations. Results are given for several large text collections in support of these claims, both for compression effectiveness and query efficiency.  相似文献   
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A pipelined architecture for distributed text query evaluation   总被引:1,自引:0,他引:1  
Two principal query-evaluation methodologies have been described for cluster-based implementation of distributed information retrieval systems: document partitioning and term partitioning. In a document-partitioned system, each of the processors hosts a subset of the documents in the collection, and executes every query against its local sub-collection. In a term-partitioned system, each of the processors hosts a subset of the inverted lists that make up the index of the collection, and serves them to a central machine as they are required for query evaluation. In this paper we introduce a pipelined query-evaluation methodology, based on a term-partitioned index, in which partially evaluated queries are passed amongst the set of processors that host the query terms. This arrangement retains the disk read benefits of term partitioning, but more effectively shares the computational load. We compare the three methodologies experimentally, and show that term distribution is inefficient and scales poorly. The new pipelined approach offers efficient memory utilization and efficient use of disk accesses, but suffers from problems with load balancing between nodes. Until these problems are resolved, document partitioning remains the preferred method. Alistair Moffat was supported by the Australian Research Council, the ARC Special Research Center for Perceptive and Intelligent Machines in Complex Environments, and the NICTA Victoria Laboratory. William Webber and Justin Zobel were supported by the Australian Research Council. Ricardo Baeza-Yates was supported by Grant P01-029-F from Millennium Initiative of Mideplan, Chile; and by the University of Melbourne as a visiting scholar at the time this project was undertaken.  相似文献   
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‘It's important that we remember the past is not just dry facts and statistics but also the detailed lives of real people. SAPPHIRE aims to give a voice to these lives.’ The Scottish Archive of Print and Publishing History Records (SAPPHIRE), an initiative with Napier University as lead and Queen Margaret University College as main collaborative partner, is an oral history project which aims to record the social, economic and cultural heritage of the Scottish printing and publishing industry in the 20th century. Undertaken in partnership with a number of Scottish organizations, its results are providing a better understanding of an important and overlooked part of Scotland's heritage. Outcomes of the project include a permanent oral history archive stored at the Edward Clark Collection at Napier University, and exhibitions and publications on the history of the printing and publishing industry. The development and current activities of SAPPHIRE are described and reviewed.  相似文献   
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Doulas, women who primarily provide social support during childbirth, have been associated with a number of positive health outcomes. Because the primary model of practice for doulas is a fee-for-service model in which families privately hire a doula, many expectant women who could benefit from doula support are unable to access the service. The Doulas Care program, located in Ann Arbor, Michigan, represents one model in which doulas provide services without charge. As a result of their extended role in the community, doulas who work with the Doulas Care program have unique educational needs. Through the use of focus groups with the program's volunteer doulas, educational needs related to overcoming barriers to being a doula working in the community were identified. Recommendations for education and training are made to improve the support doulas offer as community health outreach workers.  相似文献   
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The article relates the experiences of one large comprehensive school in its first year as a member of a pilot Local Resource Management (LRM) scheme. It considers some of the difficulties, the training implications and some of the advantages and disadvantages which have already come to light. Some advice is also given to other schools which are likely to be involved in such schemes as soon as the ‘Baker Bill’ becomes law.  相似文献   
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Outdoor education practice around the world occurs in diverse circumstances, environments and cultures. The application of outdoor education to specific cultural and environmental issues in particular places and communities has received little attention in research. While research in fields such as cultural geography has addressed the relationships between cultures, communities and geographical places, this is largely overlooked in outdoor education research. In this paper I draw on literature from cultural history and environmental history to explore how these disciplines might inform outdoor education research and pedagogy that addresses current cultural and environmental issues of specific communities and geographical places. With the aid of the rhizome metaphor for (re)structuring knowledge, I use examples from my practice in Australia to demonstrate how reading the landscape and the use of stories, or historical accounts, can assist outdoor educators and participants to probe and reflect on the relationships between personal experience and the complex cultural-ecological processes that have shaped the places in which we live and work.  相似文献   
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Simulation and analysis have shown that selective search can reduce the cost of large-scale distributed information retrieval. By partitioning the collection into small topical shards, and then using a resource ranking algorithm to choose a subset of shards to search for each query, fewer postings are evaluated. In this paper we extend the study of selective search into new areas using a fine-grained simulation, examining the difference in efficiency when term-based and sample-based resource selection algorithms are used; measuring the effect of two policies for assigning index shards to machines; and exploring the benefits of index-spreading and mirroring as the number of deployed machines is varied. Results obtained for two large datasets and four large query logs confirm that selective search is significantly more efficient than conventional distributed search architectures and can handle higher query rates. Furthermore, we demonstrate that selective search can be tuned to avoid bottlenecks, and thus maximize usage of the underlying computer hardware.  相似文献   
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This article explores the relevance of social engineering for the postindustrial epoch. The concept of social engineering has been dormant in recent years, stained by the behavior of police states in the 20th century. Yet stripped of its excesses, social engineering still represents a defensible moral and political enterprise. What is needed for the 21st century, however, is a chastened, deontological theory of social engineering, one that accepts the inviolability of the person while still pursuing ambitious long-term teleological strategies through state action. For its content, progressive information society policy should revisit the ethical norms developed by the left-liberal tradition, as articulated by the late John Rawls and others. The article concludes that the information age offers a new opportunity to engineer a just social order, or, at any rate, that the policymaking community needs to reevaluate the idea of social engineering.  相似文献   
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