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From Doug Cutting <>
Subject Re: Query optimizer - Cost of Queries
Date Mon, 29 Mar 2004 19:22:52 GMT
Jochen Frey wrote:
> I believe TermDocs(t).freq()) gives me the number of documents in which the
> term appears, as opposed to the total number of times the term appears. Any
> particular reason for choosing that metric (it seems less accurate, but
> maybe it's the only one that can be easily retrieved).

That's correct.  This is computed because it is required for IDF 
weighting, the most common a priori term weighting technique.

> As for the costs mentioned below. I'd assume that they be different from
> machine to machine.

They probably vary somewhat, but are probably fairly proportional.  If 
one factor is 100 times another on one machine, it will still probably 
be considerably larger than the other in other situations.


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