Tips on building a better BooleanQuery

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Tips on building a better BooleanQuery

Daniel Shane
Hi!

I'm planning on contributing to Lucene by adding a new kind of query. I dont
know how to call it yet, but it would be a mix of BooleanQuery and
ExactPhraseQuery.

I would like to have a Query that is a BooleanQuery, but with a slight touch
where it would boost results if it finds the query terms in a an exact
phrase.

For example, if I have terms A, B and C and I do a simple boolean search : A
B C, I would like to have a query that behaves a bit like if I rewrote this
query as such :

+A +B +C "A B" "B C" "A B C"

This would boost results where the exact string "A B C" or any substring
like "A B" or "B C" are found.

Of course I could rewrite all the queries, but it takes way too long to
search which this algorithm. I wanted to know if anyone has any ideas in
what direction I should go, or if its easy or not to implement this idea by
modifying or extending some already existing Query classes.

I'm fairly new to Lucene although I know a bit about search engines, idf,
etc... but I've tried to understand BooleanQuery and ExactPhraseQuery to see
how I could modify them and I'm having a bit of a problem understanding it
all on my own I guess.

Any help or comments would be appreciated, and if it works well I do think
it would be a good addition to the Lucene code base (I think this query
should be used as a default in the QueryParser if it works ok instead of a
simple BooleanQuery).

Thanks in advance for your help,
Daniel Shane
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Re: Tips on building a better BooleanQuery

Doug Cutting
Daniel Shane wrote:
>> For example, if I have terms A, B and C and I do a simple boolean search
> : A
> B C, I would like to have a query that behaves a bit like if I rewrote this
> query as such :
>
> +A +B +C "A B" "B C" "A B C"
>
> This would boost results where the exact string "A B C" or any substring
> like "A B" or "B C" are found.

You could extend ExactPhraseScorer and override phraseFreq() to first
compute a (weighted) sum the freq() of each TermPositions in the
PhrasePositions.  The weighting should probably be something like
sqrt(freq)/idf(term).

Doug

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