One way synonym search in Elasticsearch - elasticsearch

Question

I want to implement synonym one way search in Elasticsearch. One way search meaning if I define a => x,y,z and search for 'a', search result should include all the documents containing words x,y,z,a which is working now. But if I search for 'x' then search result should contain document which contains only 'x' and not 'a'.
Is this possible in Elasticsearch ?

Answer 1

You can not do this in a synonym relation as the behaviour you are explaining is a hyperonym/hyponym relation.
You can achieve such a behaviour on index-time though.
So for each occurrence of a you also index x,y,z. Using an additional field for this would be a good idea to not mess up the scores.
This behaviour is sadly not part of elasticsearch and has to be implemented by hand while feeding the data.

Answer 2

I've implemented one-way synonyms by inverting the synonym expression:
e.g.:
Robert => Bob, Rob
Bob => Robert
but I had to use this analyzer with synonyms is different way.
In mapping, synonyms are hooked to a new field:
"FirstName": {
"type": "string",
"analyzer": "standard",
"search_analyzer": "standard",
"fields": {
"raw": {
"type": "string",
"analyzer": "standard"
},
"synonym": {
"type": "string",
"analyzer": "firstname_synonym_analyzer"
}
}
},
And search looks like this:
"bool": {
"should": [
{
"match": {
"FirstName": {
"query": "Jo"
}
}
},
{
"match": {
"FirstName.synonym": {
"query": "Jo"
}
}
}
],
"minimum_should_match": 1
}
This way first field contains normal value, second just possible synonyms. So looking for Bob finds Robert, but not Rob.

Answer 3

I would implement it with synonyms using generic expansion aka genre expansion and different analyzers for index-time and query-time
Synonyms at index time:
Bob => Bob, Robert
Rob => Rob, Robert
The format is like
word => the same word, more generic word, even more generic, etc
Query time: no synonyms applied
Query for "Bob" will return only documents where "Bob" was.
Query for "Rob" will return only documents where "Rob" was.
Query for "Robert" will return documents where "Bob", "Rob" and "Robert" was.