5732912
Crawler-Friendly Web Servers
In this paper we study how to make web servers (e.g., Apache) more crawler friendly. Current web servers offer the same interface to crawlers and regular web surfers, even though crawlers and surfers have very different performance requirements. We evaluate simple and easy-to-incorporate modifications to web servers so that there are significant bandwidth savings. Specifically, we propose that web servers export meta-data archives decribing their content.
1713822
A fast regular expression indexing engine
In this paper; we describe the design, architecture, and lessons learned from the implementation of a fast regular-expression indexing engine FREE. FREE uses a prebuilt index to identify the text data units which may contain a matching string and only examines these further. In this way, FREE shows orders of magnitude performance improvement in certain cases over standard regular expression matching systems, such as lex, awk and grep.
2425278
Shuffling a Stacked Deck: The Case for Partially Randomized Ranking of Search Engine Results
In-degree, PageRank, number of visits and other measures of Web page popularity significantly influence the ranking of search results by modern search engines. The assumption is that popularity is closely correlated with quality, a more elusive concept that is difficult to measure directly. Unfortunately, the correlation between popularity and quality is very weak for newly-created pages that have yet to receive many visits and/or in-links. Worse, since discovery of new content is largely done by querying search engines, and because users usually focus their attention on the top few results, newly-created but high-quality pages are effectively "shut out," and it can take a very long time before they become popular.We propose a simple and elegant solution to this problem: the introduction of a controlled amount of randomness into search result ranking methods. Doing so offers new pages a chance to prove their worth, although clearly using too much randomness will degrade result quality and annul any benefits achieved. Hence there is a tradeoff between exploration to estimate the quality of new pages and exploitation of pages already known to be of high quality. We study this tradeoff both analytically and via simulation, in the context of an economic objective function based on aggregate result quality amortized over time. We show that a modest amount of randomness leads to improved search results.
516682
Efficient Crawling Through URL Ordering
In this paper we study in what order a crawler should visit the URLs it has seen, in order to obtain more "important" pages first. Obtaining important pages rapidly can be very useful when a crawler cannot visit the entire Web in a reasonable amount of time. We define several importance metrics, ordering schemes, and performance evaluation measures for this problem. We also experimentally evaluate the ordering schemes on the Stanford University Web. Our results show that a crawler with a good ordering scheme can obtain important pages significantly faster than one without.
171503
Parallel crawlers
In this paper we study how we can design an effective parallel crawler. As the size of the Web grows, it becomes imperative to parallelize a crawling process, in order to finish downloading pages in a reasonable amount of time. We first propose multiple architectures for a parallel crawler and identify fundamental issues related to parallel crawling. Based on this understanding, we then propose metrics to evaluate a parallel crawler, and compare the proposed architectures using 40 million pages collected from the Web. Our results clarify the relative merits of each architecture and provide a good guideline on when to adopt which architecture.
1739520
Exploiting Geographical Location Information of Web Pages
Many information resources on the web are relevant primarily to limited geographical communities. For instance, web sites containing information on restaurants, theaters, and apartment rentals are relevant primarily to web users in geographical proximity to these locations. In contrast, other information resources are relevant to a broader geographical community. For instance, an on-line newspaper may be relevant to users across the United States. Unfortunately, the geographical scope of web resources is largely ignored by web search engines. We make the case for identifying and exploiting the geographical location information of web sites so that web search engines can rank resources in a geographically sensitive fashion, in addition to using more traditional information-retrieval strategies. In this paper, we first consider how to compute the geographical location of web pages. Subsequently, we consider how to exploit such information in one specific "proof-of-concept" application we implemented in JAVA, and discuss other examples as well.
30800683
An optimal signal design for band-limited asynchronous DS-CDMA Communications
An optimal signal design for band-limited, asynchronous, direct-sequence code-division multiple-access (DS-CDMA) communications with aperiodic random spreading sequences and a conventional matched filter receiver is considered in an additive white Gaussian noise (AWGN) channel. With bandwidth defined in the strict sense, two optimization problems are solved under finite bandwidth and zero interchip interference constraints. First, a chip waveform optimization is performed given the system bandwidth, the data symbol transmission rate, and the processing gain. A technique to characterize a band-limited chip waveform with a finite number of parameters is developed, and it is used to derive optimum chip waveforms which minimize the effect of multiple-access interference (MAI) for any energy and delay profile of users. Next, a joint optimization of the processing gain and the chip waveform is performed, given the system bandwidth and the data symbol transmission rate. A sufficient condition for a system to have lower average probability of bit error for any energy profile is found, and it is used to derive some design strategies. It is shown that the flat spectrum pulse with the processing gain leading to zero excess bandwidth results in the minimum average probability of bit error. Design examples and numerical results are also provided.
1534837
A Parallel Execution Model of Logic Program Based on Dependency Relationship Graph
19746677
Performance analysis of an ATM switch with multiple paths
An ATM switch based on multistage interconnection networks with multiple paths can support higher bandwidth than that of buffered networks with single path by passing multiple packets to the same destination simultaneously. These multiple packets are buffered in the output buffer of the destination. The performance of output buffer in the switch with multiple paths is closely dependent on the output traffic distribution, which is the packet arrival rate at each output link destined to a given output port. As the nonuniformity of the output traffic distribution becomes higher, the performance of the output buffer as like delay and packet loss probability gets better. In this paper, we propose a new self-routing switch architecture with multiple paths called Fly network and analyze the performance of the switching network and the output buffer focusing on the output traffic distribution. It is shown that the Fly network supports best throughput and latency of the output buffer by producing a high degree of the nonuniform output traffic distribution.
3145493
KPSP: A Knowledge Programming System based on Prolog
7663373
Performance analysis of multipath multistage interconnection networks with nonuniform output traffic distribution
Develops the analysis of output buffers in multipath multistage interconnection networks. The delay-throughput performance of output buffers in multipath interconnection networks is closely related to the output traffic distribution, which is the distribution of packet arrival rates at each output link connected to a given output module. Many multipath networks produce nonuniform output traffic distributions, even if the input traffic pattern is uniform. We propose in this paper a performance model for output buffer analysis with respect to such a nonuniform output traffic distribution and analyze the output buffer performance of several multipath networks by our proposed analysis model. It is shown that the output traffic distributions are different for the various multipath networks and the output buffer performance (such as packet loss probability and delay) gets better as the nonuniformity of the output traffic distribution becomes higher.