add NGramSynonymTokenizer [LUCENE-5253]

[asfimport]

I'd like to propose that we have another n-gram tokenizer which can process synonyms. That is NGramSynonymTokenizer. Note that in this ticket, the gram size is fixed, i.e. minGramSize = maxGramSize.

Today, I think we have the following problems when using SynonymFilter with NGramTokenizer.
For purpose of illustration, we have a synonym setting "ABC, DEFG" w/ expand=true and N = 2 (2-gram).

1. There is no consensus (I think :-) how we assign offsets to generated synonym tokens DE, EF and FG when expanding source token AB and BC.
2. If the query pattern looks like XABC or ABCY, it cannot be matched even if there is a document "…XABCY…" in index when autoGeneratePhraseQueries set to true, because there is no "XA" or "CY" tokens in the index.

NGramSynonymTokenizer can solve these problems by providing the following methods.

• NGramSynonymTokenizer reads synonym settings (synonyms.txt) and it doesn't tokenize registered words. e.g.

source text	NGramTokenizer+SynonymFilter	NGramSynonymTokenizer
ABC	AB/DE/BC/EF/FG	ABC/DEFG

• The back and forth of the registered words, NGramSynonymTokenizer generates extra tokens w/ posInc=0. e.g.

source text	NGramTokenizer+SynonymFilter	NGramSynonymTokenizer
XYZABC123	XY/YZ/ZA/AB/DE/BC/EF/C1/FG/12/23	XY/YZ/Z/ABC/DEFG/1/12/23

In the above sample, "Z" and "1" are the extra tokens.

---

Migrated from LUCENE-5253 by Koji Sekiguchi (@kojisekig), resolved Oct 02 2013
Linked issues:

• add NGramSynonymTokenizer [LUCENE-5252] #6316

[asfimport]

Koji Sekiguchi (@kojisekig) (migrated from JIRA)

Sorry, duplicated.