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https://issues.apache.org/jira/browse/LUCENE-8776?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16827142#comment-16827142
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Michael Gibney commented on LUCENE-8776:
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{quote}Unfortunately, you cannot properly index a token graph: Lucene discards
the PositionLengthAttribute which is why if you really want to index a token
graph you should insert a FlattenGraphFilter at the end of your chain. This
still discards information (loses the graph-ness) but tries to do so minimizing
how queries are broken.
{quote}
Would there be any interest revisiting LUCENE-4312: adding support for indexed
position length (PositionLengthAttribute)?
Since Ram's is an index-time use case, I see only two options:
1. [~mikemccand]'s suggestion, which would compromise phrase query accuracy
(e.g., missing "light-emitting-diode glows"), and
2. [~jpountz]'s initial suggestion, which would compromise highlighting
precision.
For graph TokenStreams, indexed position length could be used to fully address
(as opposed to minimize) "how queries are broken", in addition to avoiding the
tradeoff/compromise in the case described here. It would also enable index-time
multi-term synonyms, etc ...
> Start offset going backwards has a legitimate purpose
> -----------------------------------------------------
>
> Key: LUCENE-8776
> URL: https://issues.apache.org/jira/browse/LUCENE-8776
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/search
> Affects Versions: 7.6
> Reporter: Ram Venkat
> Priority: Major
>
> Here is the use case where startOffset can go backwards:
> Say there is a line "Organic light-emitting-diode glows", and I want to run
> span queries and highlight them properly.
> During index time, light-emitting-diode is split into three words, which
> allows me to search for 'light', 'emitting' and 'diode' individually. The
> three words occupy adjacent positions in the index, as 'light' adjacent to
> 'emitting' and 'light' at a distance of two words from 'diode' need to match
> this word. So, the order of words after splitting are: Organic, light,
> emitting, diode, glows.
> But, I also want to search for 'organic' being adjacent to
> 'light-emitting-diode' or 'light-emitting-diode' being adjacent to 'glows'.
> The way I solved this was to also generate 'light-emitting-diode' at two
> positions: (a) In the same position as 'light' and (b) in the same position
> as 'glows', like below:
> ||organic||light||emitting||diode||glows||
> | |light-emitting-diode| |light-emitting-diode| |
> |0|1|2|3|4|
> The positions of the two 'light-emitting-diode' are 1 and 3, but the offsets
> are obviously the same. This works beautifully in Lucene 5.x in both
> searching and highlighting with span queries.
> But when I try this in Lucene 7.6, it hits the condition "Offsets must not go
> backwards" at DefaultIndexingChain:818. This IllegalArgumentException is
> being thrown without any comments on why this check is needed. As I explained
> above, startOffset going backwards is perfectly valid, to deal with word
> splitting and span operations on these specialized use cases. On the other
> hand, it is not clear what value is added by this check and which highlighter
> code is affected by offsets going backwards. This same check is done at
> BaseTokenStreamTestCase:245.
> I see others talk about how this check found bugs in WordDelimiter etc. but
> it also prevents legitimate use cases. Can this check be removed?
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