Xapian discuss - Sep 2008 - Making SORTAFTER useful in omega?

Hello List,

Our users keep asking for some more "logical" sorting of search
results.
Now the results are sorted on relevance, i.e. the raw weight, by 
default. But since the users only see the percentage, that results in a 
seemingly random secondary sorting.

According to the docs and earlier mails, omega has the 'SORTAFTER' (and 
docid sorting) functionality to allow date-based secondary sorting. But 
according to later mails and the documentation that's only useful if you 
don't use the default BM25-weighting. Unfortunately you can't alter the 
weighting scheme via Omega-calls.
Nor does it seem to help to simply patch query.cc to use TradWeight 
rather than BM25.

Since we've built our set-up around omega, we'd rather not have to build
something similar or patch omega just because its missing a small but 
important feature. Is it somehow possible to make the newer results in 
the seemingly similarly relevant results sort on top within Omega?

Best regards,

Arjen

Is there no one with some input on this issue?

Best regards,

Arjen

On 1-9-2008 22:43 Arjen van der Meijden wrote:
> Hello List,
> 
> Our users keep asking for some more "logical" sorting of search
results.
> Now the results are sorted on relevance, i.e. the raw weight, by 
> default. But since the users only see the percentage, that results in a 
> seemingly random secondary sorting.
> 
> According to the docs and earlier mails, omega has the 'SORTAFTER'
(and
> docid sorting) functionality to allow date-based secondary sorting. But 
> according to later mails and the documentation that's only useful if
you
> don't use the default BM25-weighting. Unfortunately you can't alter
the
> weighting scheme via Omega-calls.
> Nor does it seem to help to simply patch query.cc to use TradWeight 
> rather than BM25.
> 
> Since we've built our set-up around omega, we'd rather not have to
build
> something similar or patch omega just because its missing a small but 
> important feature. Is it somehow possible to make the newer results in 
> the seemingly similarly relevant results sort on top within Omega?
> 
> Best regards,
> 
> Arjen
> 
> _______________________________________________
> Xapian-discuss mailing list
> Xapian-discuss at lists.xapian.org
> http://lists.xapian.org/mailman/listinfo/xapian-discuss
>

On Mon, Sep 01, 2008 at 10:43:54PM +0200, Arjen van der Meijden
wrote:
> According to the docs and earlier mails, omega has the 'SORTAFTER'
(and
> docid sorting) functionality to allow date-based secondary sorting. But 
> according to later mails and the documentation that's only useful if
you
> don't use the default BM25-weighting. Unfortunately you can't alter
the
> weighting scheme via Omega-calls.
> Nor does it seem to help to simply patch query.cc to use TradWeight 
> rather than BM25.
You generally need to set the parameters to BM25Weight or TradWeight to
eliminate the effect of document length on the weight (for BM25Weight:
k2 = 0 and b = 0; for TradWeight: k = 0).

It ought to be possible to set the weighting scheme used and the
parameters to it though.  I've created a ticket for this:

http://trac.xapian.org/ticket/298

Cheers,
    Olly