lucene-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Timothy Rodriguez (BLOOMBERG/ 120 PARK)" <trodrigue...@bloomberg.net>
Subject Re: UnifiedHighlighter and extraction of exact hit offset ranges
Date Wed, 11 Jan 2017 13:45:31 GMT
While we were open sourcing it. I had tried creating a patch to generify it, but the generics
did wind up all over the place. Ultimately the UnifiedHighlighter would need to be generic
itself so it can ensure the passage formatters etc are of the same type. (Or alternatively,
generic passage formatters are passed in per request.) I wound up dumping the changes because
they were quite substantial and they'd also push it further from the PostingsHighlighjer.


I'm hoping to get back to trying that again in he future. It'd be nice to have a PassageFormatter<MyCustomObject>.


-Tim

Sent from Bloomberg Professional for iPhone

----- Original Message -----
From: Dawid Weiss <dawid.weiss@gmail.com>
To: david.w.smiley@gmail.com
CC: TIMOTHY RODRIGUEZ, dev@lucene.apache.org
At: 11-Jan-2017 08:37:37


Thanks David!

That's almost exactly what I ended up doing. I don't mind casting
Object to my own type; you can always make it a covariant override in
your subclass (which you have to do to access those expert-level
methods anyway).

I still kind of think startOffset/endOffset and other related methods
could be made public to allow tinkering with them in
FieldHighlighter#highlightOffsetsEnums (otherwise this method is
protected for overriding, but useless in practice).

There is another API problem I found too. If you wish to override
FieldHighlighter.getSummaryPassagesNoHighlight you can't return
anything sensible because Passage is final, contains only
package-private fields and addMatch is package-private too. So you
can't create a "custom" passage.

I can file an issue and provide a patch if these changes are not
against the design of the unified highlighter?

Dawid

On Wed, Jan 11, 2017 at 2:24 PM, David Smiley <david.w.smiley@gmail.com> wrote:
> Hi Dawid,
>
> You could write a trivial PassageFormatter that simply returns the Passage
> list instead of doing formatting.  Passages contain offsets. And yes,
> WholeBreakIterator if you don't need passage fragmentation. Unless I'm
> missing some aspect of your requirements, this doesn't involve any internal
> highlighter customizing.  Perhaps Javadocs could be improved to make this
> more clear... and perhaps this Passage-returning PassageFormatter could be
> included to clarify how it's done.  I recall doing or seeing this recently
> months ago but I'm not sure.
>
> One ugly aspect of the API (shared with it's PostingsHighlighter lineage)
> related to this discussion is that the PassageFormatter is declared to
> return Object.  It's kinda hard to rectify it to be typed, perhaps with
> generics, while also not spilling lots of generics to other places (the UH
> itself) just because of this.  Perhaps UH.highlightFieldsAsObjects() could
> be modified to take a Class to thus provide a type for the output... and
> maybe the PassageFormatter could declare not only with generics but with a
> method what types of results it produces.  I'm curious what you think.
>
> ~ David
>
>
> On Wed, Jan 11, 2017 at 6:02 AM Dawid Weiss <dawid.weiss@gmail.com> wrote:
>>
>> To follow-up: I hacked into the offsets by passing WholeBreakIterator
>> and a custom PassageFormatter that just returns the matches from the
>> singleton resulting passage. This is suboptimal though, as there's
>> still some complex logic going on in highlightOffsetsEnums that could
>> be avoided.
>>
>> Dawid
>>
>> On Wed, Jan 11, 2017 at 11:34 AM, Dawid Weiss <dawid.weiss@gmail.com>
>> wrote:
>> > Can any of the folks who contributed to UnifiedHighlighter (David?)
>> > clarify my thinking here?
>> >
>> > I have a requirement to extract (for a set of search results) a list
>> > of exact "hit" ranges (field offsets, with support for multi-term
>> > queries and span queries). Obviously, I'm only talking about queries
>> > that relate to field content somehow, but this has always been quite
>> > problematic and required the use of multiple helper classes
>> > (WeightedSpanTermExtractor, MultiTermHighlighting, etc.) and pretty
>> > hairy logic.
>> >
>> > So I turned to look at UnifiedHighlighter for help.
>> >
>> > Seems like the right way (?) to do it would be to override (and abuse)
>> > UnifiedHighlighter's getFieldHighlighter method and return a field
>> > highlighter with an override of:
>> >
>> > protected Passage[] highlightOffsetsEnums(List<OffsetsEnum>
>> > offsetsEnums) throws IOException {
>> >
>> > so that I can capture and return a separate Passage for each
>> > OffsetsEnum (I have my own code to deal with overlaps and merging, so
>> > I can skip this entirely). Then, with a custom no-op PassageFormatter
>> > I could simply get a list of those offsets.
>> >
>> > The problem with this approach is that there is currently no way to
>> > access offsets in OffsetsEnum -- everything is protected (so
>> > subclassable), but OffsetsEnum are closed to package-private scope.
>> > Namely these two:
>> >
>> >   int startOffset() throws IOException {
>> >     return postingsEnum.startOffset();
>> >   }
>> >
>> >   int endOffset() throws IOException {
>> >     return postingsEnum.endOffset();
>> >   }
>> >
>> > Should these two be protected to allow such customizations (I agree
>> > it's *very* low-level, but I have a practical use case where this
>> > would be useful).
>> >
>> > Am I on the right track here?
>> >
>> > Separately from that, I think it'd be nice to have some sort of
>> > generic utility that, for a given document (or a set of documents)
>> > would return such hit ranges... UnifiedHighlighter seems
>> >
>> > Dawid
>
> --
> Lucene/Solr Search Committer, Consultant, Developer, Author, Speaker
> LinkedIn: http://linkedin.com/in/davidwsmiley | Book:
> http://www.solrenterprisesearchserver.com
Mime
View raw message