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Most search engines simply look for documents that contain the words that the user enters into the search box (aka "keyword search" engines). [[Boolean search]] engines add a degree of sophistication by allowing the user to specify additional requirements but most users struggle to comprehend and use the necessary syntax (e.g. Tiger NEAR Woods AND (golf OR golfing) NOT Volkswagen). [[Phrase search]] is easier to understand but can lead to many useful documents being missed if they do not contain the exact phrase specified.
Techniques for probabilistic weighting of single word terms dates back to at least 1976 and the landmark publication by Stephen E. Robertson <ref>http://www.soi.city.ac.uk/~ser/homepage.html Stephen E. Robertson</ref> and [[Karen Spärck Jones]]: Relevance weighting of search terms originally published in the Journal of the American Society for Information Science. <ref> [http://www.soi.city.ac.uk/~ser/papers/RSJ76.pdf] Relevance weighting of search terms</ref> Robertson has stated that the assumption of word independence is not justified and exists simply as a matter of mathematical convenience. The objection to assumptions about term independence are not new, dating back to at least 1964 when H. H. Williams expressed it this way: "The assumption of independence of words in a document is usually made as a matter of mathematical convenience". <ref>WILLIAMS, J.H., 'Results of classifying documents with multiple discriminant functions', In : Statistical Association Methods for Mechanized Documentation, National Bureau of Standards, Washington, 217-224 (1965).</ref>
[[Compound term processing]] is a new approach to an old problem: how to improve the relevance of search results without missing anything important whilst maintaining ease of use. By forming compound (i.e. multi-word) terms and placing these in the search engine's index the search can be performed with a higher degree of accuracy because the ambiguity inherent in single words is no longer a problem. A search for ''survival rates following a triple heart bypass in elderly people'' will locate documents about this topic even if this precise phrase is not contained in any document. A [[concept search]] using "Compound Term Processing" can extract the key concepts automatically (in this case "survival rates", "triple heart bypass" and "elderly people") and use these to select the most relevant documents.
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