java-user  

product based term combination for BooleanQuery?

Tim Sturge
Tue, 03 Jul 2007 10:41:02 -0700

I'm following myself up here to ask if anyone has experience or code with a BooleanQuery that weights the terms it encounters on a product basis rather than a sum basis.
This would effectively compute the geometric mean of the term score (rather than the arithmetic mean) and would give me more "middle bias". It also has the great advantage that it automatically implements AND (as something without the term has a score of 0.0 which causes the query to go to 0.0 as well.)
I'm curious though why this doesn't already exist. Is it a bad idea in general (that I will discover once I implement it and look at the results?) or does it make searching a lot slower? 

Thanks,

Tim

Tim Sturge wrote:
I have an index with two different sources of information, one small but of high quality (call it "title"), and one large, but of lower quality (call it "body"). I give boosts to certain documents related to their popularity (this is very similar to what one would do indexing the web).
The problem I have is a query like "John Bush". I translate that into " (title:John^4.0 body:John) AND (title:Bush^4.0 body:Bush) ". But the results I get are: 

1. George Bush
...
4. John Kerry
...
10. John Bush

The reason is (looking at explain) that George Bush is scored:
169 = sum(
1 =  <match in body with tiny norm for "John">
)
168 = sum(
    160 = <title match for "Bush">
    8 = <body match for "Bush">
)
)

and John Kerry is similar but reversed. Poor old "John Bush" only scores:

72 = sum(
 40 = (<title match for "John">+<body match>)
 32 = (<title match for "Bush">+ <body match>)
)

because his initial boost was only 1/4 of George's.
The question I have is, how can tell the searcher to care about "balance"? I really want the score over 2 terms to be more like (sqrt(X)+sqrt(Y))^2 or maybe even exp(log(X)+log(Y)) rather than just X+Y. Is that supported in some obvious way, or is there some other way to phrase my query to say "I want both terms but they should both be important if possible?" 

Thanks,

Tim







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