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From "Peter Keegan" <peterlkee...@gmail.com>
Subject Re: Best Practices for getting Strings from a position range
Date Thu, 09 Aug 2007 20:29:08 GMT
Hi Grant,

I'm hoping to check this out soon.

Thanks,
Peter

On 8/7/07, Grant Ingersoll <gsingers@apache.org> wrote:
>
> Hi Peter,
>
> Give https://issues.apache.org/jira/browse/LUCENE-975 a try.  It
> provides a TermVectorMapper that loads by position.
>
> Still not what ideally what you want, but I haven't had time to scope
> that one out yet.,
>
> -Grant
>
> On Jul 24, 2007, at 6:02 PM, Peter Keegan wrote:
>
> > Hi Grant,
> >
> > No problem - I know you are very busy.  I just wanted to get a
> > sense for the
> > timing because I'd like to use this for a release this Fall. If I
> > can get a
> > prototype working in the coming weeks AND the performance is
> > great :) , this
> > would be terrific. If not, I'll have to fall back on a more complex
> > design
> > that handles the query outside of Lucene :(
> >
> > In the meantime, I'll try playing with LUCENE-868.
> >
> > Thanks for the update.
> > Peter
> >
> > On 7/24/07, Grant Ingersoll <grant.ingersoll@gmail.com> wrote:
> >>
> >> Sorry, Peter, I haven't had a chance to work on it.  I don't see it
> >> happening this week, but maybe next.
> >>
> >> I do think the Mapper approach via TermVectors will work.  It will
> >> require implementing a new mapper that orders by position, but I
> >> don't think that is too hard.   I started on one on the LUCENE-868
> >> patch (version 4) but it is not complete.  Maybe you want to pick
> >> it up?
> >>
> >> With this approach, you would iterate your spans, when you come to a
> >> new doc, you would load the term vector using the PositionMapper, and
> >> then you could index into the positions for the matches in the
> >> document.
> >>
> >> I realize this does not cover the just wanting to get the Payload at
> >> the match issue.  Maybe next week...
> >>
> >> Cheers,
> >> Grant
> >>
> >> On Jul 23, 2007, at 8:51 AM, Peter Keegan wrote:
> >>
> >> > Any idea on when this might be available (days, weeks...)?
> >> >
> >> > Peter
> >> >
> >> > On 7/16/07, Grant Ingersoll <gsingers@apache.org> wrote:
> >> >>
> >> >>
> >> >> On Jul 16, 2007, at 1:06 AM, Chris Hostetter wrote:
> >> >>
> >> >> >
> >> >> > : Do we have a best practice for going from, say a SpanQuery
> >> doc/
> >> >> > : position information and retrieving the actual range of
> >> >> positions of
> >> >> > : content from the Document?  Is it just to reanalyze the
> >> Document
> >> >> > : using the appropriate Analyzer and start recording once you
> >> >> hit the
> >> >> > : positions you are interested in?    Seems like Term Vectors
> >> >> _could_
> >> >> > : help, but even my new Mapper approach patch (LUCENE-868)
> >> doesn't
> >> >> > : really help, because they are stored in a term-centric
> >> manner.  I
> >> >> > : guess what I am after is a position centric approach.  That
> >> >> is, give
> >> >> >
> >> >> > this is kind of what i was suggesting in the last message i sent
> >> >> > to the java-user thread about paylods and SpanQueries (which i'm
> >> >> > guessing is what prompted this thread as well)...
> >> >> >
> >> >> > http://www.nabble.com/Payloads-and-PhraseQuery-
> >> >> > tf3988826.html#a11551628
> >> >>
> >> >>
> >> >> This is one use case, the other is related to the new patch I
> >> >> submitted for LUCENE-960.  In this case, I have a SpanQueryFilter
> >> >> that identifies a bunch of docs and positions ahead of time.  Then
> >> >> the user enters new Span Query and I want to relate the matches
> >> from
> >> >> the user query with the positions of matches in the filter and
> >> then
> >> >> show that window.
> >> >>
> >> >> >
> >> >> > my point was that currently, to retrieve a payload you need a
> >> >> > TermPositions instance, which is designed for iterating in the
> >> >> > order of...
> >> >> >     seek(term)
> >> >> >       skipTo(doc)
> >> >> >          nextPosition()
> >> >> >             getPayload()
> >> >> > ...which is great for getting the payload of every instance
> >> >> > (ie:position) of a specific term in a given document (or in
> >> every
> >> >> > document) but without serious changes to the Spans API, the
> >> ideal
> >> >> > payload
> >> >> > API would let you say...
> >> >> >     skipTo(doc)
> >> >> >        advance(startPosition)
> >> >> >          getPayload()
> >> >> >        while (nextPosition() < endPosition)
> >> >> >          getPosition()
> >> >> >
> >> >> > but this seems like a nearly impossible API to implement
> >> given the
> >> >> > natore
> >> >> > of hte inverted index and the fact that terms aren't ever
> >> stored in
> >> >> > position order.
> >> >> >
> >> >> > there's a lot i really don't know/understand about the lucene
> >> term
> >> >> > position internals ... but as i recall, the datastructure
> >> written
> >> >> > to disk
> >> >> > isn't actually a tree structure inverted index, it's a long
> >> >> > sequence of
> >> >> > tuples correct?  so in theory you could scan along the tuples
> >> >> > untill you
> >> >> > find the doc you are interested in, ignoring all of the term
> >> info
> >> >> > along
> >> >> > the way, then whatever term you happen be on at the moment, you
> >> >> > could scan
> >> >> > along all of the positions until you find one in the range
> >> you are
> >> >> > interested in -- assuming you do, then you record the current
> >> Term
> >> >> > (and
> >> >> > read your payload data if interested)
> >> >>
> >> >> I think the main issue I see is in both the payloads and the
> >> matching
> >> >> case above is that they require a document centric approach.  And
> >> >> then, for each Document,
> >> >> you ideally want to be able to just index into an array so that
> >> you
> >> >> can go directly to the position that is needed based on
> >> >> Span.getStart()
> >> >>
> >> >> >
> >> >> > if i remember correctly, the first part of this is easy, and
> >> >> > relative fast
> >> >> > -- i think skipTo(doc) on a TermDoc or TermPositions will
> >> happily
> >> >> > scan for
> >> >> > the first <term,doc> pair with the correct docId,
> >> irregardless of
> >> >> > the term
> >> >> > ... the only thing i'm not sure about is how efficient it is to
> >> >> > loop over
> >> >> > nextPosition() for every term you find to see if any of them
> >> are in
> >> >> > your
> >> >> > range ... the best case scenerio is that the first position
> >> >> > returned is
> >> >> > above the high end of your range, in which case you can stop
> >> >> > immediately
> >> >> > and seek to the next term -- butthe worst case is that you call
> >> >> > nextPosition() over an over a lot of times before you get a
> >> >> > position in
> >> >> > (or above) your rnage .... an advancePosition(pos) that
> >> wokred like
> >> >> > seek
> >> >> > or skipTo might be helpful here.
> >> >> >
> >> >> > : I feel like I am missing something obvious.  I would
> >> suspect the
> >> >> > : highlighter needs to do this, but it seems to take the
> >> reanalyze
> >> >> > : approach as well (I admit, though, that I have little
> >> experience
> >> >> > with
> >> >> > : the highlighter.)
> >> >> >
> >> >> > as i understand it the default case is to reanalyze, but if you
> >> >> have
> >> >> > TermFreqVector info stored with positions (ie: a
> >> >> > TermPositionVector) then
> >> >> > it can use that to construct a TokenStream by iterating over all
> >> >> > terms and
> >> >> > writing them into a big array in position order (see the
> >> >> > TermSources class
> >> >> > in the highlighter)
> >> >>
> >> >>
> >> >> Ah, I see that now.  Thanks.
> >> >> >
> >> >> > this makes sense when highlighting because it doesn't know what
> >> >> > kind of
> >> >> > fragmenter is going to be used so it needs the whole
> >> TokenStream,
> >> >> > but it
> >> >> > seems less then ideal when you are only interested in a small
> >> >> > number of
> >> >> > position ranges that you know in advance.
> >> >> >
> >> >> > : I am wondering if it would be useful to have an alternative
> >> Term
> >> >> > : Vector storage mechanism that was position centric.
> >> Because we
> >> >> > : couldn't take advantage of the lexicographic compression, it
> >> >> would
> >> >> > : take up more disk space, but it would be a lot faster for
> >> these
> >> >> > kinds
> >> >> >
> >> >> > i'm not sure if it's really neccessary to store the data in a
> >> >> position
> >> >> > centric manner, assuming we have a way to "seek" by position
> >> like i
> >> >> > described above -- but then again i don't really know that
> >> what i
> >> >> > described above is all that possible/practical/performant.
> >> >> >
> >> >>
> >> >> I suppose I could use my Mapper approach to organize things in a
> >> >> position centric way now that I think about it more.  Just
> >> means some
> >> >> unpacking and repacking.  Still, probably would perform well
> >> enough
> >> >> since I can setup the correct structure on the fly.  I will
> >> give this
> >> >> a try.  Maybe even add a Mapper to do this.
> >> >>
> >> >>
> >> >> -Grant
> >> >>
> >> >>
> >> ---------------------------------------------------------------------
> >> >> To unsubscribe, e-mail: java-dev-unsubscribe@lucene.apache.org
> >> >> For additional commands, e-mail: java-dev-help@lucene.apache.org
> >> >>
> >> >>
> >>
> >> ------------------------------------------------------
> >> Grant Ingersoll
> >> http://www.grantingersoll.com/
> >> http://lucene.grantingersoll.com
> >> http://www.paperoftheweek.com/
> >>
> >>
> >>
> >> ---------------------------------------------------------------------
> >> To unsubscribe, e-mail: java-dev-unsubscribe@lucene.apache.org
> >> For additional commands, e-mail: java-dev-help@lucene.apache.org
> >>
> >>
>
> --------------------------
> Grant Ingersoll
> http://lucene.grantingersoll.com
>
> Lucene Helpful Hints:
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>
>
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