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https://issues.apache.org/jira/browse/LUCENE-8717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16806850#comment-16806850
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Alan Woodward commented on LUCENE-8717:
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{{StopFilter}} extends {{FilteringTokenFilter}} so it will handle things in the
same way. I've gone back and forth a bit on whether we should use
{{TermDeletedAttribute}} all the time, or whether we can restrict it to just
articulation points, but I think we should probably do the latter.
Articulation points will only appear in token graphs, and there are a whole
bunch of token filters that don't really make sense in that context, so with
this change we only need to update a few filters; if we extend it so that
everything needs to understand TermDeletedAttribute then there are a whole
bunch of filters that we need to update (for example, all the
summarizing/hashing filters - do we include deleted terms or not here?)
For synonyms, this still doesn't quite work because of the way SynonymMap
builds itself, but I think cutting SynonymGraphFilter over to use
GraphTokenFilter will make it a lot easier to match multi-token inputs with
stopwords. That would be a separate issue though.
> Handle stop words that appear at articulation points
> ----------------------------------------------------
>
> Key: LUCENE-8717
> URL: https://issues.apache.org/jira/browse/LUCENE-8717
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Alan Woodward
> Assignee: Alan Woodward
> Priority: Major
> Attachments: LUCENE-8717.patch, LUCENE-8717.patch
>
>
> Our set of TokenFilters currently cannot handle the case where a multi-term
> synonym starts with a stopword. This means that given a synonym file
> containing the mapping "the walking dead => twd" and a standard english
> stopword filter, QueryBuilder will produce incorrect queries.
> The tricky part here is that our standard way of dealing with stopwords,
> which is to just remove them entirely from the token stream and use a larger
> position increment on subsequent tokens, doesn't work when the removed token
> also has a position length greater than 1. There are various tricks you can
> do to increment position length on the previous token, but this doesn't work
> if the stopword is the first token in the token stream, or if there are
> multiple stopwords in the side path.
> Instead, I'd like to propose adding a new TermDeletedAttribute, which we only
> use on tokens that should be removed from the stream but which hold necessary
> information about the structure of the token graph. These tokens can then be
> removed by GraphTokenStreamFiniteStrings at query time, and by
> FlattenGraphFilter at index time.
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