[jira] [Commented] (LUCENE-6664) Replace SynonymFilter with SynonymGraphFilter

["Robert Muir (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-6664?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14642694#comment-14642694 ] 

Robert Muir commented on LUCENE-6664:
-------------------------------------

So is positionlength still (ab)used as really a node ID? Should it use another attribute instead?

> Replace SynonymFilter with SynonymGraphFilter
> ---------------------------------------------
>
>                 Key: LUCENE-6664
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6664
>             Project: Lucene - Core
>          Issue Type: New Feature
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: 5.3, Trunk
>
>         Attachments: LUCENE-6664.patch, LUCENE-6664.patch, usa.png, usa_flat.png
>
>
> Spinoff from LUCENE-6582.
> I created a new SynonymGraphFilter (to replace the current buggy
> SynonymFilter), that produces correct graphs (does no "graph
> flattening" itself).  I think this makes it simpler.
> This means you must add the FlattenGraphFilter yourself, if you are
> applying synonyms during indexing.
> Index-time syn expansion is a necessarily "lossy" graph transformation
> when multi-token (input or output) synonyms are applied, because the
> index does not store {{posLength}}, so there will always be phrase
> queries that should match but do not, and then phrase queries that
> should not match but do.
> http://blog.mikemccandless.com/2012/04/lucenes-tokenstreams-are-actually.html
> goes into detail about this.
> However, with this new SynonymGraphFilter, if instead you do synonym
> expansion at query time (and don't do the flattening), and you use
> TermAutomatonQuery (future: somehow integrated into a query parser),
> or maybe just "enumerate all paths and make union of PhraseQuery", you
> should get 100% correct matches (not sure about "proper" scoring
> though...).
> This new syn filter still cannot consume an arbitrary graph.



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