DiscoWeb: Applying Link Analysis to Web Search

Extended Abstract (2 pages) Postscript (70KB) PDF (15KB)
Poster Slides (17 pages, 519KB)
Brian. D. Davison, Apostolos Gerasoulis, Konstantinos Kleisouris, Yingfang Lu, Hyun-ju Seo, Wei Wang, and Baohua Wu
Department of Computer Science, Rutgers University

Extended Abstract

How often does the search engine of your choice produce results that are less than satisfying, generating endless links to irrelevant pages even though those pages may contain the query keywords? How often are you given pages that tell you things you already know? While the search engines and related tools continue to make improvements in their information retrieval algorithms, for the most part they continue to ignore an essential part of the web - the links. We have found that link analysis can have significant contributions to web page retrieval from search engines, to web community discovery, and to the measurement of web page influence. It can help to rank results and find high-quality index/hub/link pages that contain links to the best sites on the topic of interest.

Our work is based on research from IBM's CLEVER project [7, 4, 6], Stanford's Google [3 ], and the Web Archaeology research [2, 1] at Compaq's Systems Research Center. These research teams have demonstrated some of the contributions that link analysis can make in the web. In our work, we have attempted to generalize and improve upon these approaches. Just as in citation analysis of published works, the most influential documents on the web will have many other documents recommending (pointing to) them. This idea underlies all link analysis efforts, from the straightforward technique of counting the number of incoming edges to a page, to the deeper eigenvector analysis used in our work and in those projects mentioned above.

It turns out that the identification of ``high-quality'' web pages reduces to a sparse eigenvalue of the adjacency matrix of the linked graph [7, 3]. In 1998, Kleinberg [7] provided the analysis and substantial evidence that each eigenvector creates a web clustering which he called ``web communities''. The most important web community corresponds to the principal eigenvector and the component values within each eigenvector represent a ranking of web pages. Determining the eigenvectors is computationally intensive since the linked graph can be quite large, e.g. each keyword search could result in millions of page hits. For this reason, the approach taken in most implementations is to determine only the principal eigenvector [7, 3], using the well-known power iterative method [5] for eigenvectors. If the initial approximation is the unit vector then the first iteration in the power method corresponds to the counting of the incoming and/or outgoing edges for each page of the web graph. There are certain advantages and disadvantages of this approach that we discuss below:

At Rutgers we have built a prototype called DiscoWeb that consists of a generalization of the method proposed by Kleinberg [7], a page retriever and graph generator, with a Java interface. DiscoWeb determines up to the top 1/4 eigenvalues and eigenvectors associated with the graph. We use an eigenvalue solver that converges quickly, less than a minute for 100 eigenvectors on graphs on the order of 10000 nodes. Preliminary results show a very promising method. By looking at a larger set of eigenvectors we can find clusterings of web pages that are more interesting than the ones extracted by the principal eigenvector (similar to the conclusions derived in the original Kleinberg paper). We can then use heuristics to extract a global ranking as well as local rankings given by each eigenvector community.

For example, Chakrabarti et. al. [4] concluded that the principal eigenvector for the ARC method, a weighted extension of Kleinberg's power method, scores relatively poorly for the query affirmative action as compared to human-edited directories provided by Infoseek and Yahoo. When our prototype was applied to this query, using AltaVista as the source of the pages, the ranking produced many pages that were highly ranked in the Infoseek and Yahoo directories. This result was generated from a rather small sample (only 2211 pages in the neighborhood of the query results). How to select an appropriate eigenvector is still an open research question. We are currently using a heuristic that looks at the highest ranked pages in each eigenvector. For example, what is often considered the ``best'' page for the affirmative action query (www.auaa.org) is highly rated in eigenvectors other than the first (2nd, 3rd, etc. depending on DiscoWeb parameters). This page might have been missed if the principal eigenvector were the only one considered because its ranking value is close to zero in that eigenvector.

We believe that there is much promise in the use of link analysis for improving search engine retrievals as well as other tasks. Some of the results that DiscoWeb has produced are quite striking. For example for the query cancer, DiscoWeb has found all the three star sites that have been selected by the editors of the Infoseek directory, plus many other important pages. On the other hand AltaVista found only few of the three star Infoseek sites. There are, however, many problems that need to be addressed before run-time link analysis can be incorporated into interactive search engine queries. The most important one is the reduction of the computational and retrieval time of the method. An interactive search engine requires response time in seconds. The current DiscoWeb implementation takes few minutes, for graphs of sizes of the order of 10000, which is beyond the interactive search engine constraints. We are currently investigating the reduction of computational and retrieval time via parallelization. However, even in its current form, DiscoWeb can be extremely useful in building high quality web directories automatically, where time constraints are not as strict as those of interactive search engines [4].


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Poster presented at the Eighth International World Wide Web Conference, Toronto, May 11-14, 1999. Extended abstract included on pages 148-149 of the poster proceedings.

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Last modified: 13 January 2001
Brian D. Davison