[Xapian-devel] GSoC 2011 Weighting Schemes

[wuwenjin]

As described in http://terrier.org/docs/current/dfr_description.html, there
are many DFR models, which models will to be implemented in Xapian.

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*Wenjin Wu*




2011/3/28 Olly Betts <olly at survex.com>

> On Mon, Mar 28, 2011 at 10:24:30AM +0800, wuwenjin wrote:
> > I have great interested in "Weight Schemes" project. and in the last few
> > days I have learnt some detail about DFR model family by reading some
> papers
> > and web page. I find that Terrier Project (http://terrier.org/)  has
> > implement most of DFR scheme in Java language
>
> Yes, Terrier implements a number of DfR schemes.
>
> > and  briefly read related
> > source of Terrier's package( org.terrier.matching.models), I think
> "weight
> > scheme" can imitate that package, of course in C++.
>
> Xapian's weighting schemes are structured in a particular way to allow
> for various optimisations.  You need to subclass Xapian::Weight and
> implement various methods to implement them, so I would suggest just
> starting from the formulae - trying to directly translate Terrier's code
> to C++ will give you Java-esque C++ code which doesn't actually fit where
> you need it.
>
> You can see the Xapian::Weight API here:
>
> http://trac.xapian.org/browser/trunk/xapian-core/include/xapian/weight.h
>
> > It will be better to
> > implement a generic DFR  weighting model allowing any DFR to be generated
> > and evaluated. Since DFR is a framework  or model family, which contains
> > many basic models and different normalizations.
>
> An interesting idea.
>
> Although it's a family of weighting schemes, I suspect you'd find you
> ended up switching between different implementations for each DfR scheme
> internally, and that's better done by subclassing really.
>
> But probably worth thinking about further.
>
> Cheers,
>     Olly
>
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