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From Shai Erera <ser...@gmail.com>
Subject Re: Proposal: Scorer api change
Date Tue, 08 Jun 2010 16:45:08 GMT
Well … I don't know the reason as well and always thought Scorer and
Similarity are confusing.

But Scorer is itself an iterator, so what prevents you from calling
nextDoc and advance on it without score(). And what would the returned
DISI do when nextDoc is called, if not delegate to its subs?

If I were in your shoes, I'd simply provider a Query wrapper. If CSQ
is not good enough I'd just develop my own.

But perhaps others think differently?

Shai

On Tuesday, June 8, 2010, John Wang <john.wang@gmail.com> wrote:
> Hi Shai:
>     I am not sure I understand how changing Similarity would solve this problem, wouldn't
you need the reader?
>     As for PayloadTermQuery, payload is not always the most efficient way of storing
such data, especially when number of terms << numdocs. (I am not sure accessing the
payload when you iterate is a good idea, but that is another discussion)
>
>     Yes, what I described is exactly a simple CustomScoreQuery for a special use-case.
The problem is also in CustomScoreQuery, where nextDoc and advance are calling the sub-scorers
as a wrapper. This can be avoided if the Scorer returns an iterator instead.
>
>     Separating scoring and doc iteration is a good idea anyway. I don't know the reason
to combine them originally.
> Thanks
> -John
>
>
> On Tue, Jun 8, 2010 at 8:47 AM, Shai Erera <serera@gmail.com> wrote:
>
> So wouldn't it make sense to add some method to Similarity? Which receives the doc Id
in question maybe ... just thinking here.
>
> Factoring Scorer like you propose would create 3 objects for scoring/iterating: Scorer
(which really becomes an iterator), Similarity and CustomScoreFunction ...
>
> Maybe you can use CustomScoreQuery? or PayloadTermQuery? depends how you compute your
age decay function (where you pull the data about the age of the document).
>
> Shai
>
>
> On Tue, Jun 8, 2010 at 6:41 PM, John Wang <john.wang@gmail.com> wrote:
> Hi Shai:
>     Similarity in many cases is not sufficient for scoring. For example, to implement
age decaying of a document (very useful for corpuses like news or tweets), you want to project
the raw tfidf score onto a time curve, say f(x), to do this, you'd have a custom scorer that
decorates the underlying scorer from your say, boolean query:
>
>
>
> public float score(){    return myFunc(innerScorer.score());}
>     This is fine, but then you would have to do this as well:
> public int nextDoc(){
>
>
>    return innerScorer.nextDoc();}
> and also:
> public int advance(int target){   return innerScorer.advance();}      The difference
here is that nextDoc and advance are called far more times as score. And you are introducing
an extra method call for them, which is not insignificant for queries result in large recall
sets.
>
>
>
> Hope this makes sense.
> Thanks
> -John
> On Tue, Jun 8, 2010 at 5:02 AM, Shai Erera <serera@gmail.com> wrote:
> I'm not sure I understand what you mean - Scorer is a DISI itself, and the scoring formula
is mostly controlled by Similarity.
>
> What will be the benefits of the proposed change?
>
> Shai
>
> On Tue, Jun 8, 2010 at 8:25 AM, John Wang <john.wang@gmail.com> wrote:
>
>
>
>
> Hi guys:
>
>     I'd like to make a proposal to change the Scorer class/api to the following:
>
>
> public abstract class Scorer{
>    DocIdSetIterator getDocIDSetIterator();
>    float score(int docid);
> }
>
> Reasons:
>
> 1) To build a Scorer from an existing Scorer (e.g. that produces raw scores from tfidf),
one would decorate it, and it would introduce overhead (in function calls) around nextDoc
and advance, even if you just want to augment the score method which is called much fewer
times.
>
> 2) The current contract forces scoring on the currentDoc in the underlying iterator.
So once you pass "current", you can no longer score. In one of our use-cases, it is very inconvenient.
>
> What do you think? I can go ahead and open an issue and work on a patch if I get some
agreement.
>
> Thanks
>
> -John
>
>
>
>
>
>
>
>
>

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