[Koha-devel] Stemming and zebra

[David Cook]

Hi Francois:

 

I wrote an email earlier on my tablet, but not 100% sure if it got sent. In any case, I’m writing again now!

You’ll want to look at C4::Search::_build_stemmed_operand().

 

Zebra doesn’t actually do any stemming itself. If you read through the Zebra docs (if you’re masochistic), you’ll notice that they say explicitly that Zebra doesn’t do any stemming, but that you can do stemming (using a stemmer like Snowball) while building a query. That’s exactly what we do in Koha.

 

The Perl module that does the stemming is Lingua::Stem::Snowball. 

 

However, you might notice that your query’s operands aren’t always stemmed properly. I haven’t looked in a while, but I think it’s because we don’t build our queries very well at all (when not using QueryParser). 

 

If you want to understand why you’re getting “skills” and “fishxsdfe” in your results, I would suggest running some tests ( using “Data::Dumper” and “warn” ) so that you can see your query as it is built.

 

I have a lot of work I want to do on C4::Search::buildQuery, but just don’t have the time :/.

 

Unfortunately, at the moment, there is no stemming when using the QueryParser. However, fortunately, using Lingua::Stem::Snowball with QueryParser would be really really easy. I think that I’ve written a note on how to do that somewhere on Bugzilla or maybe on Trello…

I hope that helps! Feel free to send me an email or shout at me on IRC if you want any clarification. I know I probably didn’t make it any clearer but hopefully this might help you on your path to understanding.

 

David Cook

Systems Librarian

Prosentient Systems

72/330 Wattle St, Ultimo, NSW 2007

 

From: koha-devel-bounces at lists.koha-community.org [mailto:koha-devel-bounces at lists.koha-community.org] On Behalf Of Francois Charbonnier
Sent: Wednesday, 27 August 2014 2:09 AM
To: koha-devel at lists.koha-community.org
Subject: [Koha-devel] Stemming and zebra

 

Hello,

I have tested the QueryStemming system preference on Koha 3.14 (my local installation) and I'm wondering, does zebra just right truncate the words or is there an algorithm to find the stems?

I use ICU and I have enabled "QueryWeightFields". I don't have automatic truncation or fuzzy search on. I use these words for my tests:

*	ski, skiing, skills
*	fish, fished, fishing, fisher, fishxsdfe

Each time, with QueryStemming on, skills and fishxsdfe come out in the search results. Is it what I should expect? "Skills", maybe but "fishxsdfe"?

Do you know how it works? or have a good example that would help me to understand?

Thanks!

-- 

François Charbonnier,
Bibl. prof. / Chef de produits

Tél.  : (888) 604-2627
 <mailto:francois.charbonnier at inLibro.com> francois.charbonnier at inLibro.com 

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