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https://issues.apache.org/jira/browse/LUCENE-2470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12869302#action_12869302
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Robert Muir commented on LUCENE-2470:
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{quote}
I think we should allow the conditional to switch between
sub-pipelines? EG I could make a stage that detects proper names
(say)... and if the token is not a proper name, it'll run through a
LowercaseFilter then StopFilter, else it passes through. So the
conditional would switch between full sub-pipelines.
{quote}
I really like this aspect of the idea. Besides the language issues that
Steven brought up, we could start to look at the KeywordAttribute/KeywordMarker
as a "hack", and this is a more generalized way to look at it.
I think the real key is, if we can make it nice to do this declaratively,
for example in a Solr schema definition.
This way, someone with a multilanguage document/query could apply
conditional pipelines to different parts, someone could do the 'keyword'
stuff (but this might be based on length, their own custom attribute, POS,
whatever they want).
In truth I think there are a lot of hardcoded 'conditions/parameters' in the
analysis components right now. Something like this would allow pieces to
be more general/reusable and flexible.
> Add conditional braching/merging to Lucene's analysis pipeline
> --------------------------------------------------------------
>
> Key: LUCENE-2470
> URL: https://issues.apache.org/jira/browse/LUCENE-2470
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Analysis
> Affects Versions: 4.0
> Reporter: Steven Rowe
> Priority: Minor
>
> Captured from a #lucene brainstorming session with Robert Muir:
> Lucene's analysis pipeline would be more flexible if it were possible to
> apply filter(s) to only part of an input stream's tokens, under
> user-specifiable conditions (e.g. when a given token attribute has a
> particular value) in a way that did not place that responsibility on
> individual filters.
> Two use cases:
> # StandardAnalyzer could directly handle ideographic characters in the same
> way as CJKTokenizer, which generates bigrams, if it could call ShingleFilter
> only when the TypeAttribute=<CJK>, or if Robert's new
> ScriptAttribute=<Ideographic>.
> # Stemming might make sense for some stemmer/domain combinations only when
> token length exceeds some threshold. For example, a user could configure an
> analyzer to stem only when CharTermAttribute length is greater than 4
> characters.
> One potential way to achieve this conditional branching facility is with a
> new kind of filter that can be configured with one or more following filters
> and condition(s) under which the filter should be engaged. This could be
> called BranchingFilter.
> I think a MergingFilter, the inverse of BranchingFilter, is necessary in the
> current pipeline architecture, to have a single pipeline endpoint. A
> MergingFilter might be useful in its own right, e.g. to collect document data
> from multiple sources. Perhaps a conditional merging facility would be
> useful as well.
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