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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-6582) SynonymFilter should generate a correct (or, at least, better) graph
Date Thu, 18 Jun 2015 21:04:01 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-6582?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14592501#comment-14592501
] 

Michael McCandless commented on LUCENE-6582:
--------------------------------------------

Just to confirm the scope of this change, if I have these synonyms:

{noformat}
  wtf --> what the fudge
  wtf --> wow that's funny
{noformat}

And then I'm tokenizing this:

{noformat}
  wtf happened
{noformat}

Before this change (today) I get this crazy sausage incorrectly
matching phrases like "wtf the fudge" and "wow happened funny":

!before.png!

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

!after.png!

Matching exactly the right phrases?  Note that absolute position
numbers become somewhat meaningless now ... they are really "node
IDs".

Some small things I noticed:

{noformat}
       originalInputIdx = -10;
{noformat}

Why -10?

Can we just add the new test cases into the existing (tiny)
TestMultiWordSynonyms.java?

Related: LUCENE-5012 is an effort to make such "graph consuming and
producing token streams" easier ... but that's a major change to the
TokenStream API.

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())?


> SynonymFilter should generate a correct (or, at least, better) graph
> --------------------------------------------------------------------
>
>                 Key: LUCENE-6582
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6582
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Ian Ribas
>         Attachments: LUCENE-6582.patch, after.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: https://github.com/elastic/elasticsearch/issues/10394).
> 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|https://issues.apache.org/jira/browse/LUCENE-6400?focusedCommentId=14498554&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14498554]).
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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