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From Stefan Trcek <>
Subject Concerning LUCENE-3079: Facetiing module
Date Tue, 21 Jun 2011 18:17:07 GMT

I can donate our facette module to the lucene project.

The implementation relies on field cache only, no index scheme, no 
cached filters etc. It is small (about 600 lines of code in 10 
classes). I didn't measure performance, but it handles 1Mio documents 
(30GB) without problems. I suppose it might fit the requirements 
described in LUCENE-3079.

The module supports
- single valued facets
- multi valued facets
- facet filters
- evaluation of facet values that would dismiss due to other facet 

Let me explain the last point: For the user a facet query
  (color==green) AND (shape==circle OR shape==square)
may look like

Facet color
[ ] (3) red
[x] (5) green
[ ] (7) blue

Facet shape
[x] (9) circle
[ ] (4) line
[x] (2) square

The red/blue/line facet values will display even though the 
corresponding documents are not in the result set. Also there is 
support for filtered facet values with zero results, so users 
understand why they do not get results.

So how to start? Preparing a patch against trunk (currently it is 3.1)?

Stefan Trcek

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