Latent Semantic Indexing
Promising technique for search engines. "Regular keyword searches approach a document collection with a kind of accountant mentality: a document contains a given word or it doesn't, with no middle ground. Latent semantic indexing adds an important step to the document indexing process. In addition to recording which keywords a document contains, the method examines the document collection as a whole, to see which other documents contain some of those same words. LSI considers documents that have many words in common to be semantically close, and ones with few words in common to be semantically distant."