I've had a nearly identical experience to what Dave describes, I also chafe under this restriction.
On Thu, Aug 6, 2020 at 11:07 AM David Smiley <dsmi...@apache.org> wrote: > I sympathize with your pain, Roman. > > It appears we can't really do index-time multi-word synonyms because of > the offset ordering rule. But it's not just synonyms, it's other forms of > multi-token expansion. Where I work, I've seen an interesting approach to > mixed language text analysis in which a sophisticated Tokenizer effectively > re-tokenizes an input multiple ways by producing a token stream that is a > concatenation of different interpretations of the input. On a Lucene > upgrade, we had to "coarsen" the offsets to the point of having highlights > that point to a whole sentence instead of the words in that sentence :-(. > I need to do something to fix this; I'm trying hard to resist modifying our > Lucene fork for this constraint. Maybe instead of concatenating, it might > be interleaved / overlapped but the interpretations aren't necessarily > aligned to make this possible without risking breaking position-sensitive > queries. > > So... I'm not a fan of this constraint on offsets. > > ~ David Smiley > Apache Lucene/Solr Search Developer > http://www.linkedin.com/in/davidwsmiley > > > On Thu, Aug 6, 2020 at 10:49 AM Roman Chyla <roman.ch...@gmail.com> wrote: > >> Hi Mike, >> >> Yes, they are not zero offsets - I was instinctively avoiding >> "negative offsets"; but they are indeed backward offsets. >> >> Here is the token stream as produced by the analyzer chain indexing >> "THE HUBBLE constant: a summary of the hubble space telescope program" >> >> term=hubble pos=2 type=word offsetStart=4 offsetEnd=10 >> term=acr::hubble pos=0 type=ACRONYM offsetStart=4 offsetEnd=10 >> term=constant pos=1 type=word offsetStart=11 offsetEnd=20 >> term=summary pos=1 type=word offsetStart=23 offsetEnd=30 >> term=hubble pos=1 type=word offsetStart=38 offsetEnd=44 >> term=syn::hubble space telescope pos=0 type=SYNONYM offsetStart=38 >> offsetEnd=60 >> term=syn::hst pos=0 type=SYNONYM offsetStart=38 offsetEnd=60 >> term=acr::hst pos=0 type=ACRONYM offsetStart=38 offsetEnd=60 >> term=space pos=1 type=word offsetStart=45 offsetEnd=50 >> term=telescope pos=1 type=word offsetStart=51 offsetEnd=60 >> term=program pos=1 type=word offsetStart=61 offsetEnd=68 >> >> Sometimes, we'll even have a situation when synonyms overlap: for >> example "anti de sitter space time" >> >> "anti de sitter space time" -> "antidesitter space" (one token >> spanning offsets 0-26; it gets emitted with the first token "anti" >> right now) >> "space time" -> "spacetime" (synonym 16-26) >> "space" -> "universe" (25-26) >> >> Yes, weird, but useful if people want to search for `universe NEAR >> anti` -- but another usecase which would be prohibited by the "new" >> rule. >> >> DefaultIndexingChain checks new token offset against the last emitted >> token, so I don't see a way to emit the multi-token synonym with >> offsetts spanning multiple tokens if even one of these tokens was >> already emitted. And the complement is equally true: if multi-token is >> emitted as last of the group - it trips over `startOffset < >> invertState.lastStartOffset` >> >> >> https://github.com/apache/lucene-solr/blame/master/lucene/core/src/java/org/apache/lucene/index/DefaultIndexingChain.java#L915 >> >> >> -roman >> >> On Thu, Aug 6, 2020 at 6:17 AM Michael McCandless >> <luc...@mikemccandless.com> wrote: >> > >> > Hi Roman, >> > >> > Hmm, this is all very tricky! >> > >> > First off, why do you call this "zero offsets"? Isn't it "backwards >> offsets" that your analysis chain is trying to produce? >> > >> > Second, in your first example, if you output the tokens in the right >> order, they would not violate the "offsets do not go backwards" check in >> IndexWriter? I thought IndexWriter is just checking that the startOffset >> for a token is not lower than the previous token's startOffset? (And that >> the token's endOffset is not lower than its startOffset). >> > >> > So I am confused why your first example is tripping up on IW's offset >> checks. Could you maybe redo the example, listing single token per line >> with the start/end offsets they are producing? >> > >> > Mike McCandless >> > >> > http://blog.mikemccandless.com >> > >> > >> > On Wed, Aug 5, 2020 at 6:41 PM Roman Chyla <roman.ch...@gmail.com> >> wrote: >> >> >> >> Hello devs, >> >> >> >> I wanted to create an issue but the helpful message in red letters >> >> reminded me to ask first. >> >> >> >> While porting from lucene 6.x to 7x I'm struggling with a change that >> >> was introduced in LUCENE-7626 >> >> (https://issues.apache.org/jira/browse/LUCENE-7626) >> >> >> >> It is believed that zero offset tokens are bad bad - Mike McCandles >> >> made the change which made me automatically doubt myself. I must be >> >> wrong, hell, I was living in sin the past 5 years! >> >> >> >> Sadly, we have been indexing and searching large volumes of data >> >> without any corruption in index whatsover, but also without this new >> >> change: >> >> >> >> >> https://github.com/apache/lucene-solr/commit/64b86331c29d074fa7b257d65d3fda3b662bf96a#diff-cbdbb154cb6f3553edff2fcdb914a0c2L774 >> >> >> >> With that change, our multi-token synonyms house of cards is falling. >> >> >> >> Mike has this wonderful blogpost explaining troubles with multi-token >> synonyms: >> >> >> http://blog.mikemccandless.com/2012/04/lucenes-tokenstreams-are-actually.html >> >> >> >> Recommended way to index multi-token synonyms appears to be this: >> >> >> https://stackoverflow.com/questions/19927537/multi-word-synonyms-in-solr >> >> >> >> BUT, but! We don't want to place multi-token synonym into the same >> >> position as the other words. We want to preserve their positions! We >> >> want to preserve informaiton about offsets! >> >> >> >> Here is an example: >> >> >> >> * THE HUBBLE constant: a summary of the HUBBLE SPACE TELESCOPE program >> >> >> >> This is how it gets indexed >> >> >> >> [(0, []), >> >> (1, ['acr::hubble']), >> >> (2, ['constant']), >> >> (3, ['summary']), >> >> (4, []), >> >> (5, ['acr::hubble', 'syn::hst', 'syn::hubble space telescope', >> 'hubble'']), >> >> (6, ['acr::space', 'space']), >> >> (7, ['acr::telescope', 'telescope']), >> >> (8, ['program']), >> >> >> >> Notice the position 5 - multi-token synonym `syn::hubble space >> >> telescope` token is on the first token which started the group >> >> (emitted by Lucene's synonym filter). hst is another synonym; we also >> >> index the 'hubble' word there. >> >> >> >> if you were to search for a phrase "HST program" it will be found >> >> because our search parser will search for ("HST ? ? program" | "Hubble >> >> Space Telescope program") >> >> >> >> It simply found that by looking at synonyms: HST -> Hubble Space >> Telescope >> >> >> >> And because of those funny 'syn::' prefixes, we don't suffer from the >> >> other problem that Mike described -- "hst space" phrase search will >> >> NOT find this paper (and that is a correct behaviour) >> >> >> >> But all of this is possible only because lucene was indexing tokens >> >> with offsets that can be lower than the last emitted token; for >> >> example 'hubble space telescope' wil have offset 21-45; and the next >> >> emitted token "space" will have offset 28-33 >> >> >> >> And it just works (lucene 6.x) >> >> >> >> Here is another proof with the appropriate verbiage ("crazy"): >> >> >> >> >> https://github.com/romanchyla/montysolr/blob/master/contrib/adsabs/src/test/org/apache/solr/analysis/TestAdsabsTypeFulltextParsing.java#L618 >> >> >> >> Zero offsets have been working wonderfully for us so far. And I >> >> actually cannot imagine how it can work without them - i.e. without >> >> the ability to emit a token stream with offsets that are lower than >> >> the last seen token. >> >> >> >> I haven't tried SynonymFlatten filter, but because of this line in the >> >> DefaultIndexingChain - I'm convinced the flatten symbol is not going >> >> to do what we need (as seen in the example above) >> >> >> >> >> https://github.com/apache/lucene-solr/blame/master/lucene/core/src/java/org/apache/lucene/index/DefaultIndexingChain.java#L915 >> >> >> >> What would you say? Is it a bug, is it not a bug but just some special >> >> usecase? If it is a special usecase, what do we need to do? Plug in >> >> our own indexing chain? >> >> >> >> Thanks! >> >> >> >> -roman >> >> >> >> --------------------------------------------------------------------- >> >> To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org >> >> For additional commands, e-mail: dev-h...@lucene.apache.org >> >> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org >> For additional commands, e-mail: dev-h...@lucene.apache.org >> >> -- http://www.needhamsoftware.com (work) http://www.the111shift.com (play)
