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From "Ian Ribas (JIRA)" <>
Subject [jira] [Commented] (LUCENE-6582) SynonymFilter should generate a correct (or, at least, better) graph
Date Fri, 19 Jun 2015 02:29:01 GMT


Ian Ribas commented on LUCENE-6582:

> But after this change, the expanded synonyms become separate paths in
> the graph right? So it will look like this?
> Matching exactly the right phrases? 

Actually, I think it looks more like this:


That means that "wtf the fudge" and "wow happened funny" will no longer match, but "wow the
fudge" would.

The absolute positions still have meaning. I couldn't figure out how to clearly separate the
two phrases from the rules (as was mentioned on the TODO comment above) using the token attributes.
They will be stacked in the same order on each position, but that doesn't seem to be enough
to make things unambiguous. Specially since with rules like:

pass, ticket
cheap, unexpensive

and tokenizing:

cheap pass

I would expect to mach all the resulting combinations: "cheap pass", "unexpensive pass", "cheap
ticket" and "unexpensive ticket". And there is no difference in the representation of the
tokens "unexpensive" as a synonym for "cheap" from "wow" as a synonym for "what" on the previous
rules, using the attributes.

> Why -10?

I was unsure if -1 as an invalid value was clear enough and ended up using -10. It could probably
just be -1. I'll check.

> Can we just add the new test cases into the existing (tiny)

Probably. Since all tests in the new file use the new constructor to force the new behavior,
and TestMultiWordSynonyms tests the old behavior, I didn'tt want to mix things. But I'll just
join them, with a comment on the test to make it clear its the old behavior.

> In the case where a given input token matches no rules in the FST, are
> we still able to pass that through to the output without buffering
> (calling capture())?

I didn't test this specifically, but would think yes. The new behavior only handles matches
differently, I didn't have to do any extra buffering before the match, nor did I change anything
on the matching part of the code. The extra buffering is needed only when there was already
buffering (lookahead for a partial match) and the synonym was longer than the match.

> SynonymFilter should generate a correct (or, at least, better) graph
> --------------------------------------------------------------------
>                 Key: LUCENE-6582
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Ian Ribas
>         Attachments: LUCENE-6582.patch, after.png, after2.png, before.png
> Some time ago, I had a problem with synonyms and phrase type queries (actually, it was
elasticsearch and I was using a match query with multiple terms and the "and" operator, as
better explained here:
> That issue led to some work on Lucene: LUCENE-6400 (where I helped a little with tests)
and  LUCENE-6401. This issue is also related to LUCENE-3843.
> Starting from the discussion on LUCENE-6400, I'm attempting to implement a solution.
Here is a patch with a first step - the implementation to fix "SynFilter to be able to 'make
positions'" (as was mentioned on the [issue|]).
In this way, the synonym filter generates a correct (or, at least, better) graph.
> As the synonym matching is greedy, I only had to worry about fixing the position length
of the rules of the current match, no future or past synonyms would "span" over this match
(please correct me if I'm wrong!). It did require more buffering, twice as much.
> The new behavior I added is not active by default, a new parameter has to be passed in
a new constructor for {{SynonymFilter}}. The changes I made do change the token stream generated
by the synonym filter, and I thought it would be better to let that be a voluntary decision
for now.
> I did some refactoring on the code, but mostly on what I had to change for may implementation,
so that the patch was not too hard to read. I created specific unit tests for the new implementation
({{TestMultiWordSynonymFilter}}) that should show how things will be with the new behavior.

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