Search (3 results, page 1 of 1)

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Abstract

This article will examine the Z39.50 Information Retrieval protocol. It will look at some of the history of the protocol, its operation, and some of the major projects that have made use of it. There has been enough written (perhaps too much) about Z39.50 in the last several years so it is not intended to be a tutorial or detailed description of the protocol. The material that will be presented will try and put some context around the discussion. For those readers who are interested in delving into Z39.50 in a more technical manner, references to much of the material that has been written about it over the years will be provided at the end. Finally, the article will conclude with some thoughts on how technology and technological infrastructure have changed in the years since Z39.50 was initially developed and deployed, and where the protocol has so far lived up to its goals, and where it has perhaps failed to meet some of the high expectations that at least some people involved in the Z39.50 community held for it. The article will conclude with some of the author's speculations (and they are really no more than that) of what the future role of Z39.50 is likely to be.

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Abstract

Information retrieval (IR) protocols support effective and interoperable intersystem search and retrieval. Although intersystem search methods have been envisioned and under development since the 1970s, it was the Z39.50 IR protocol, first released in 1988, that demonstrated real-world possibilities for such search and retrieval. As the networked information environment changed with the emergence of the World Wide Web, the need for standard IR protocols did not disappear, and one can argue the need is even more compelling given both the visible and invisible Web. A new protocol, based on the experience from Z39.50 but simpler and more comprehensible than Z39.50, is now being used for Web search and retrieval. Search and retrieve via URL (SRU) uses Web technologies and standards resulting in a Web friendly protocol that provides standard search access to existing Z39.50 resources and a wide-range of new non-catalog digital resources. This entry provides both an overview of the two protocols and technical details to understand both. A brief discussion of IR and communications protocols provides background to the specifics of these two IR protocols. Although communication protocols are by their nature technical specifications, this entry focuses on an overview of the functions and capabilities of the protocols. It uses technical concepts and terminology from the protocols to help explain how the protocols work but limits discussion of technical details.

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Abstract

Hinich and Molyneux review the literature of internet measurement and note three results consistently to be found in network traffic studies. These are "self-similarity," "long-range dependence," by which is meant that events in one time are correlated with events in a previous time and remain so through longer time periods than expected, and "heavy tails" by which they mean many small connections with low byte counts and a few long connections with large byte counts. The literature also suggests that conventional time series analysis is not helpful for network analysis. Using a single day's traffic at the Berkeley National Labs web server, cumulated TCP flows were collected, log transforms were used with the adding of .01 to all values allowing log transforms of the zero values, and providing a distribution that overcomes the heavy tail problem. However, Hinich's bicorrelation test for nonlinearity using overlapping moving windows found strong evidence of nonlinear structures. Time series analysis assumes linear systems theory and thus additivity and scalability. Spectral analysis should provide large peaks at the lowest frequencies if long range dependence is present since the power spectrum would go to infinity if the frequency goes to zero. This does not occur and so long range dependence must be questioned, at least until it is determined what effect other OSI layers may have on the TCP data.