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From "Michael Busch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1448) add getFinalOffset() to TokenStream
Date Mon, 17 Nov 2008 19:55:44 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12648290#action_12648290
] 

Michael Busch commented on LUCENE-1448:
---------------------------------------

{quote}
Hmm we could do that... but it seems awkward to add new attributes that apply only to ending
state of the tokenizer.
{quote}

Yeah. Also you wouldn't want to pay overhead in TokenFilters that can buffer tokens to serialize
or clone those attributes for every token.

{quote}
I wonder if instead, w/ the new API, we could simply allow querying of certain attributes
(offset, posincr) after incrementToken returns "false"?
{quote}

Yeah, maybe we can make the AttributeSource more sophisticated, so that it can distinguish
between per-field (instance) and per-token attributes. But as a separate patch, not as part
of LUCENE-1422.

{quote}
Why don't you commit the new TokenStream API first, and we can iterate on this issue &
commit 2nd?
{quote}

OK, will do. I think 1422 is ready now.

> add getFinalOffset() to TokenStream
> -----------------------------------
>
>                 Key: LUCENE-1448
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1448
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Analysis
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.9
>
>         Attachments: LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch, LUCENE-1448.patch
>
>
> If you add multiple Fieldable instances for the same field name to a document, and you
then index those fields with TermVectors storing offsets, it's very likely the offsets for
all but the first field instance will be wrong.
> This is because IndexWriter under the hood adds a cumulative base to the offsets of each
field instance, where that base is 1 + the endOffset of the last token it saw when analyzing
that field.
> But this logic is overly simplistic.  For example, if the WhitespaceAnalyzer is being
used, and the text being analyzed ended in 3 whitespace characters, then that information
is lost and then next field's offsets are then all 3 too small.  Similarly, if a StopFilter
appears in the chain, and the last N tokens were stop words, then the base will be 1 + the
endOffset of the last non-stopword token.
> To fix this, I'd like to add a new getFinalOffset() to TokenStream.  I'm thinking by
default it returns -1, which means "I don't know so you figure it out", meaning we fallback
to the faulty logic we have today.
> This has come up several times on the user's list.

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