add CHANGES entry
git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/flexscoring@1167281 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 55192fa..b9f22fa 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -487,6 +487,34 @@
* LUCENE-3376: ReusableAnalyzerBase has been moved from modules/analysis/common
into lucene/src/java/org/apache/lucene/analysis (Chris Male)
+* LUCENE-2959: Added a variety of different relevance ranking systems to Lucene.
+
+ - Added Okapi BM25, Language Models, Divergence from Randomness, and
+ Information-Based Models. The models are pluggable, support all of lucene's
+ features (boosts, slops, explanations, etc) and queries (spans, etc).
+
+ - All models default to the same index-time norm encoding as DefaultSimilarity:
+ so you can easily try these out/switch back and forth/run experiments and
+ comparisons without reindexing. Note: most of the models do rely upon index
+ statistics that are new in Lucene 4.0, so for existing 3.x indexes its a good
+ idea to upgrade your index to the new format with IndexUpgrader first.
+
+ - Added a new subclass SimilarityBase which provides a simplified API
+ for plugging in new ranking algorithms without dealing with all of the
+ nuances and implementation details of Lucene.
+
+ - Added a new helper class BasicSimilarityProvider that just applies one
+ scoring algorithm to all fields, with queryNorm() and coord() returning 1.
+ In general, it is recommended to disable coord() when using the new models.
+ For example, to use BM25 for all fields:
+ searcher.setSimilarityProvider(new BasicSimilarityProvider(new BM25Similarity()));
+
+ If you instead want to apply different similarities (e.g. ones with different
+ parameter values or different algorithms entirely) to different fields, implement
+ SimilarityProvider with your per-field logic.
+
+ (David Mark Nemeskey via Robert Muir)
+
Optimizations
* LUCENE-2588: Don't store unnecessary suffixes when writing the terms
