[LUCENE-5252] add NGramSynonymTokenizer

• Type: New Feature
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: modules/analysis
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Koji Sekiguchi
• Created: 02/Oct/13 08:44
• Updated: 28/Aug/22 13:54

Description

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 ABCY, it cannot be matched even if there is a document "…ABCY…" in index when autoGeneratePhraseQueries set to true, because there is no "CY" token (but "GY" is there) 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.

Issue Links

• is duplicated by: LUCENE-5253 add NGramSynonymTokenizer