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From LSI to PLSI

Probabilistic Latent Semantic Indexing (Hofmann 1999) (Note: Hofmann has a very concise writing style. This summary thus contains passages which are more or less directly copied from Hofmann's paper, simply because you could not summarise them any further. This is just to point out in all clarity that everything in this summary represents Hofmann's work (without making direct "quotations" explicit)).
Problem Statement Hofmann proposes probabilistic latent semantic indexing, which builds on the method by Deerwester et al. (1990). The main difference is that Hofmann's method has a solid statistical foundation and that it performs significantly better on term matching tasks. The problem statement is similar: in human machine-interaction, the challenge is to retrieve relevant documents and present those to the user after he or she has formulated a request. These requests are often stated as a natural language query, within which the user enters some keywords and/or f…
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