Latent Semantic Indexing: "LATENT SEMANTIC INDEXING

Taking a Holistic View

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. We create a result set by looking through each document in turn for certain keywords and phrases, tossing aside any documents that don't contain them, and ordering the rest based on some ranking system. Each document stands alone in judgement before the search algorithm - there is no interdependence of any kind between documents, which are evaluated solely on their contents."

Huge document on how Google works... very sizable article, very interesting but, very long!