Using SweetSpotSimilarity for Solr Fulltext Indexing

(A Public Service Message)

Jay LukerSAO/NASA Astrophysics Data System

http://adsabs.harvard.edu/

From http://lucene.apache.org/java/2_9_3/api/all/org/apache/lucene/search/Similarity.html

Score for a particular

result

Buncha stuff you probably ought to read up on.

"encapsulates a few (indexing

time) boost and length factors"

{

norm(t,d)

Includes... ● Document boost - e.g. <doc boost="2.5"> ● Field boost - e.g. <field boost="3.0">

and what we're concerned with...

● lengthNorm(field) - computed at index time based on the number of tokens in the field of the input document.

These factors, multiplied together, make up the norm(t,d) for a given document

lengthNorm(String fieldName, int numTokens)"Matches in longer fields are less precise, so implementations of this method usually return smaller values when numTokens is large, and larger values when numTokens is small."

Translation:

SHORTER DOCUMENTS SCORE HIGHER

from the javadoc:

changes this ...

to this ...

lengthNorm(L) = 1

sqrt(L)

SweetSpotSimilarity

lucene/contrib/misc/...

lengthNorm(L) =1

sqrt(steepness*(|L-min|+|L-max|-(max-min))+1)

min/max = your "sweet spot" range. Lengths within this range compute to a constant, i.e., 1. steepness = controls the curve up to and down from the sweet spot "plateau".

(termcounts for all ADS's searchable fulltext since 01/2000)

<similarity class="org.ads.solr.SweetSpotSimilarityFactory"> <str name="min">1000</str> <str name="max">20000</str> <str name="steepness">0.5</str> </similarity>

In schema.xml

public class SweetSpotSimilarityFactory extends SimilarityFactory {

public static final Logger log = \ LoggerFactory.getLogger(SolrResourceLoader.class);

@Override public Similarity getSimilarity() { SweetSpotSimilarity sim = new SweetSpotSimilarity();

int max = this.params.getInt("max"); int min = this.params.getInt("min"); float steepness = this.params.getFloat("steepness");

log.info("max: " + max); log.info("min: " + min); log.info("steepness: " + steepness);

// yuck! hardcoded field settings for now sim.setLengthNormFactors("body", min, max, steepness, true); return sim; }}

Thanks!

Further reading: "Lucene and Juru at TREC 2007: 1-Million Queries Track"

http://trec.nist.gov/pubs/trec16/papers/ibm-haifa.mq.final.pdf

Also, check out our Blacklight beta search!http://labs.adsabs.harvard.edu/fulltext