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From Ype Kingma <ykin...@xs4all.nl>
Subject Re: String similarity search vs. typcial IR application...
Date Sat, 07 Jun 2003 04:16:30 GMT
On Thursday 05 June 2003 14:12, Jim Hargrave wrote:
> Our application is a string similarity searcher where the query is an input
> string and we want to find all "fuzzy" variants of the input string in the
> DB.  The Score is basically dice's coefficient: 2C/Q+D, where C is the
> number of terms (n-grams) in common, Q is the number of unique query terms
> and D is the number of unique document terms. Our documents will be
> sentences.
>
> I know Lucene has a fuzzy search capability - but I assume this would be
> very slow since it must search through the entire term list to find
> candidates.

Fuzzy search is not as fast as searching with direct terms or truncation,
but it does not search _all_ the terms.

> In order to do the calculation I will need to have 'C' - the number of
> terms in common between query and document. Is there an API that I can call
> to get this info? Any hints on what it will take to modify Lucene to handle
> these kinds of queries?

Have a look at the coord() call in the Similarity interface of Lucene 1.3.
It gets called per document with overlap and nr. of query terms when you
search with your own similarity implementation. It's based on terms
and not on n-grams, so it might be no good in your case.
You might try indexing a 1-gram as a Lucene Term.
In case a 1-gram is pnly C, A, T or G (DNA proteins) this might be too much
overhead for Lucene to handle...

Good luck,
Ype


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