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From Michael McCandless <>
Subject Re: Faceted search in OR
Date Fri, 25 Jan 2013 21:23:26 GMT
On Fri, Jan 25, 2013 at 3:48 PM, Nicola Buso <> wrote:

> if you have experiences in this use case can you share solutions? What
> is reusable from Lucene 4.x implementation?

Sorry, no experience doing drill sideways w/ Lucene facets ... just in
a prior life (another search engine).

One conceptual way to get the counts is to do "hold one out" query for
each dimension you need the sideways counts on.  EG if user searched
for "cameras", then drilled down on "Manufacturer = Sony" and drilled
down again on "FormFactor = SLR", you could do 3 queries:

  * cameras AND Manufacturer=Sony --> sideways counts for "FormFactor"

  * cameras AND FormFactor=SLR -> sideways counts for "Manufacturer"

  * cameras AND FormFactor=SLR AND Manufacturer=Sony -> query results

I believe that will work?  But it's sort of costly ... you could "save
the facet counts from the last query" to save on one of these query

Conceptually, the query divides all documents into 3 sets: document
matches (add to drill-down counts), document is a near miss (would
match except for exactly one of drill-down constraints), document
doesn't match.  The sideways counts amounts to tallying up the near
miss hits against the dimension that was the near miss.

Like if you could run a query for cameras AND (Manufacturer=Sony OR
FormFactor=SLR minShouldMatch=N-1 (1 in this case)), which would match
the "matches" and the near misses, and then during collection
determine whether it was a hit or a near miss (hmm this isn't so hard:
use Scorer.getChildren()), and collect and/or tally up the appropriate
counts (drill down or sideways), then you'd get the right counts I

I think this could be a reasonable way to do drill sideways!

> Reading some books I just noticed that the expected behaviour for an
> user filtering by facets is:
> - facet values in the same facet group (category in lucene) are added in
> OR
> - facet values from different facet groups are added in AND


> - another interesting aspect is how the selection affect the counting in
> other facets

This is why you have to do the N-1 queries I think.

> Should be interesting to evaluate if some of these facet navigation
> patterns can be implemented or supported with some utilities in Lucene
> 4.0

I think drill sideways is possible!  Just not implemented yet ...

Mike McCandless

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