Based on our discoveries, we will be implementing a BM25/Rocchio expansion model.  Garrick has a preliminary implementation using Lucene 6.6, see NDS-829.

This task is to implement Rocchio expansion using the ElasticSearch plugin framework prototyped in NDS-840.

Note:

• As a first step, our plugin just does expansion: given an original query, return the expanded query
• We need to be able to demonstrate support for expansion over different elasticsearch indexes (e..g, BioCADDIE, PubMed, Wikipedia)