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From "Russell M. Allen" <Russell.Al...@aebn.net>
Subject RE: Scoring a document (count?)
Date Mon, 31 Jul 2006 14:35:50 GMT
Thank you for the reply Doran!  You are exactly right about the sql
count(*).  I need the equivalent of group by, and count().

We have considered a 'joined' index where we would have a document for
each permutation.  We discarded it (possibly prematurely) based on the
rapid explosion in the number of documents.  In our domain, we have
movies as the main document type, and 5 other satellite document types
with their own indexes: Star, Studio, Director, Series, and Category
(genre).  With the exception of series, a movie has a many to many
relationship with the other indexes.  So, with 60k movies, 20k stars, 2k
studios, ... The document count quickly shoots through the roof.

Also, the majority of our searching is based on a single domain type,
such as movie.  It is only a small handful of corner cases where we want
what amounts to a joined query.  If we merged these indexes, we would
constantly have to 'roll up' the results into distinct instances of a
type.  (The equivalent of an SQL 'group by')


I find the parallels between the expressiveness of Lucene and SQL
interesting.  I'm glad to see you compared what I was looking for to an
sql count(*) as well.  We have a handful of indexing issues that I am
attempting to solve/optimize, of which performing a count(*) is only
one.  I also have the need to perform a JOIN across two indexes.  I have
'ideas' about how I might go about this, but for now we are fortunate
enough to have fairly static data and half of the join is static.  As a
result we can cache a bitset filter for the results of half the join and
apply it to the other (dynamic) half of the join query.

Anyway, I digress...

I saw you second post regarding creating a scorer.  I'd like to continue
down that path.  My main issue now is simply understanding how lucene
works under the covers enough to write the TermQuery variant.

Thanks for the help,
Russell.


-----Original Message-----
From: Doron Cohen [mailto:DORONC@il.ibm.com] 
Sent: Friday, July 28, 2006 3:19 AM
To: java-user@lucene.apache.org
Subject: Re: Scoring a document (count?)

This task reminds me more of a count(*) sql query than a text search
query.

Assuming that using a text search engine is a pre requisite, I can think
of two approaches - basing on Lucene scoring as suggested in the
question, or a more simple approach (below).

For the scoring approach - I don't see an easy way to get the counts
from the score of the results, although the TF (term frequency in
candidate
docs) is known+used during document scoring, and although it seems that
the application can be arranged such that TF of search result documents
would be the required count.

But perhaps a more straight forward solution can do - adding a Lucene
document for each star-movie pair. This would also allow easy update
when a new movie arrives: just add a document for each "star" in that
movie. A document can have these fields:
   StarFirstName - stored, untokenized
   StarLastName - stored, untokenized
   MovieName - stored, tokenized
   MovieType - stored, untokenized - this is the pre-computed type
mentioned below
   MovieProps  - unstored, tokenized - the word "horror" can appear in
this field, avoiding a pre-computation step.
Now a single search can do all the work:
   +StarLastName:A* +MovieProps:horror
Sorting results by StarLastName would group all results of same "star"
and also allow to count them for each star.

This would create more documents in the index -  #stars * |#movies per
star| - so there may be performance considerations, depending on the 
star| volume
of the data...

Regards,
Doron

"Russell M. Allen" <Russell.Allen@aebn.net> wrote on 27/07/2006
09:02:46:

> I am curious about the potential use of document scoring as a means to

> extract additional data from an index.  Specifically, I would like the

> score to be a count of how many times a particular field matched a set

> of terms.
>
> For example, I am indexing movie-stars (Each document is a
movie-star).
> A movie-star has a number of fields, such as name, movies they have 
> been in, etc.  I want to produce an 'index' of stars by name and show 
> how many movies, which match a filter, that they have appeared in.
>
> In natural language my query might be:
>    "List all stars who have appeared in a 'horror' movie, where last 
> name starts with A, and tell me how many horror movies they were in."
>
> My search will look something like this:
>    "+lastName:A* +movie:(1 7 21 58 92)"   //where movie is a
> previously computed list of 'horror' movie ids
>
> If my index contained the following documents:
>     doc1 = lastName:Anna   movie:{3 10}
>     doc2 = lastName:Aba    movie:{1 10 12}
>     doc3 = lastName:Addd   movie:{3 21 55 92}
>     doc4 = lastName:Baaa   movie:{7 56}
>
> I would like to get back:
>     doc2, score of 1   //score of 1 because only movie 1 matched
>     doc3, score of 2   //score of 2 because movies 21 and 92 matched
>
>
>
> Currently, we perform an initial query against our Star index to 
> retrieve a list of stars.  Then we perform N queries against a 
> separate movie index to count the number of movies that match our sub 
> filter 'horror'.  This is obviously very inefficient, and as I've 
> shown above, the information (count) is available during the primary
query.
>
> Thoughts?
>
>
>
>
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