Ryan Ernst created LUCENE-5207:
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Summary: lucene expressions module
Key: LUCENE-5207
URL: https://issues.apache.org/jira/browse/LUCENE-5207
Project: Lucene - Core
Issue Type: New Feature
Reporter: Ryan Ernst
Expressions are geared at defining an alternative ranking function (e.g.
incorporating the text relevance score and other field values/ranking
signals). So they are conceptually much more like ElasticSearch's scripting
support (http://www.elasticsearch.org/guide/reference/modules/scripting/) than
solr's function queries.
Some additional notes:
* In addition to referring to other fields, they can also refer to other
expressions, so they can be used as "computed fields".
* You can rank documents easily by multiple expressions (its a SortField at the
end), e.g. Sort by year descending, then some function of score price and time
ascending.
* The provided javascript expression syntax is much more efficient than using a
scripting engine, because it does not have dynamic typing (compiles to .class
files that work on doubles). Performance is similar to writing a custom
FieldComparator yourself, but much easier to do.
* We have solr integration to contribute in the future, but this is just the
standalone lucene part as a start. Since lucene has no schema, it includes an
implementation of Bindings (SimpleBindings) that maps variable names to
SortField's or other expressions.
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