All right. So it is still not clear how to exactly implement it.
I have SimilarityA and SimilarityB subclasses. So far, I know I can customize the similarity class for the searcher: searcher.setSimilarity(new BoostingSimilarity()); When/how should I use get method ? Similarity get(String field) thanks On 3 March 2011 16:34, Robert Muir <rcm...@gmail.com> wrote: > On Thu, Mar 3, 2011 at 10:25 AM, Patrick Diviacco > <patrick.divia...@gmail.com> wrote: > > I've downloaded Lucene nightly build because I need to customize the > > similarity *per field*. > > > > However I don't see the field parameter passed to the methods to compute > the > > score such as "tf" and "idf"... > > > > how can I implement different similarities score per document field then > ? > > > > Hi, the way you set this up is to use SimilarityProvider to configure > Similarities per-field: for example maybe field A, B, and C use > Similarity1 and field D use Similarity2. > So you just set your SimilarityProvider on the IndexWriter and > IndexSearcher, and it must implement this factory method: > > Similarity get(String field) > > Here are the reasons for this factory design (versus simply adding > field to every method): > 1. performance: up-front we ask the SimilarityProvider for the > per-field Similarity. So you probably use a hashmap or something here > to return the correct one. If you had to do this on every single call > to tf(), this would slow down queries significantly. > 2. flexibility: we are working to generalize Similarity, and maybe the > existing stuff you see becomes TFIDFSimilarity. So in the future you > might have field1 that uses TFIDF and field2 that uses something else > (e.g. BM25), with a totally different API and scoring system. > > --------------------------------------------------------------------- > To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org > For additional commands, e-mail: java-user-h...@lucene.apache.org > >
