http://www.smartwikisearch.com/ http://www.smartwikisearch.com/about.html "Smart Wiki Search uses the link structure of Wikipedia to calculate which concepts each page is associated with. It is easy to see why looking at links can help group pages by concepts. For example, pages about mathematics have a lot of links to (and from) other pages about mathematics. Pages about the Apollo moon landing have a lot of links to pages about NASA and pages about the moon, etc. "More specifically, Smart Wiki Search uses the so-called eigendecomposition of the Wikipedia link transition matrix. Eigendecomposition provides of a number of special vectors, called eigenvectors, and their corresponding eigenvalues. These vectors are special because even a relatively small number of eigenvectors having the largest eigenvalues can capture all the most important properties of the link structure. "It is well-known that Google uses the eigenvector with the largest eigenvalue (the so-called primary eigenvector) to rank pages in their search results. Any other eigenvector cannot be used for ranking or scoring the pages, however they can still carry almost as much information as the primary eigenvector, and they can be very effectively used for grouping pages. Smart Wiki Search uses ~1,100 eigenvectors with the largest eigenvalues. The primary eigenvector is discarded. More information about the algorithm can be found on the Algorithm page. "The algorithm only uses the link structure and page titles to perform the search. It does not use terms or keywords that it encounters on the page. Because there is no need to determine what the meaning of the particular term or keyword is, the pages it returns generally deal with the same concept or concepts that you entered. For instance, if you enter "Flower" and "Bee", it will find pages where these two concepts overlap - those are pages about pollination. Compare these results to a typical keyword search (Google, for instance: Flower, bee, site:en.wikipedia.org), and you will see just how much less focussed on the concepts the keyword search is." - d.