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From "Erick Erickson" <erickerick...@gmail.com>
Subject relevancy "buckets" and secondary searching
Date Mon, 05 Feb 2007 21:45:02 GMT
Am I missing anything obvious here and/or what would folks suggest...

Conceptually, I want to normalize the scores of my documents during a search
BUT BEFORE SORTING into 5 discrete values, say 0.1, 0.3, 0.5, 0.7, 0.9 and
apply a secondary sort when two documents have the same score. Applying the
secondary sort is easy, it's massaging the scores that has me stumped.

We have a bunch of documents (30K). Books actually. We only display to the
user 5 different "relevance" scores, with 5 being the most relevant. So far,
so good.

Within each quintile, we want to sort by title. So, suppose the following
three books score a hit:

relevance      title
0.98              zzzzz
0.94              ccccc
0.79              aaaaa

The proper display would be

5           ccccc
5           zzzzz
4           aaaaa


It's easy enough to do a secondary sort, but that would not give me what I
want. In this case, I'd get...

5       zzzzz
5       ccccc
4       aaaaa

because the secondary sort only matters if the primary sort is equal. The
user is left scratching her head asking "why did two books with the same
relevancy have the titles out of order?".

If I could massage my scores *before* sorts are done, things would be
hunky-dory, but I'm not seeing how to do that. One problem is that until the
top N documents have been collected, I don't know what the maximum relevance
is, therefore I don't know how to normalize raw scores. I followed Hoss's
thread where he talks about FakeNorms, but don't see how that applies to my
problem.

My result sets are strictly limited to < 500, so it's not unreasonable to
just get the TopDocs back and aggregate my buckets at that point and sort
them. But of course I only care about this when I am using relevancy as my
primary sort. For sorting on any other fields, I would just let Lucene take
care of it all. So post-sorting myself leads to really ugly stuff like

if (it's my special relevancy sort) do one thing
else don't do that thing.

repeated wherever I have to sort. Yuck.....


And since I'm talking about 500 docs, I don't want to wait until after I
have a Hits object because I'll have to re-query several times. On an 8G
index (and growing).


This almost looks like a HitCollector, but not quite.
This almost looks like a custom Similarity, but not quite since I want to
just let Lucene compute relevance and put that into a bucket.
This almost looks like FakeNorms, but not quite.
This almost looks like about 8 things I tried to make work, but not quite
<G>....

So, somebody out there needs to tell me what part of the manual I overlooked
<G>...

Thanks
Erick

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