Re: [Tracker] question of tracker sparql query multi langauge order

[Carlos Garnacho <carlos lanedo com>]

Hey,

On mar, 2013-05-28 at 13:55 +0100, Martyn Russell wrote:
> On 22/05/13 16:45, Eugene Seo wrote:
> > Dear all,
>
> Hello Eugene,
>
> > I have a question of tracker sparql query order with multi langauges.
> > Currently tracker supports Sparql  1.0 and sorts the result in unicode
> > order, as I know.
>
> Yes it does.
>
> > Is it possible to sort other language prior to English?
>
> Usually sorting by different languages is done by the locale 
> settings/environment. Sorting by language per query isn't currently 
> possible because we build collations based on the language being used. 
> If you change language, we rebuild those collations in the database.
>
> > In SQLite, specific chacracters can be sorted in front with following
> > syntax,
> > ORDER BY (CASE WHEN str between '0' and '9' THEN 1 WHEN str between 'a'
> > and 'z' THEN 2 ELSE 3 END)
>
> This is pretty cool and I didn't know about this I have to say.

I'm wondering though, doesn't this kill ordering between items of the
same group? If everything from A to Z is 2, the ordering would be
arbitrary there AFAICS.

> > I wonder there is similar syntax of SPARQL query like CASE WHEN THEN of
> > SQLITE.
>
> Well, the SPARQL in Tracker is interpreted, some of it (like ORDER BY) 
> is used directly for the SQL used in SQLite. I haven't actually tried 
> the example you suggest above, have you? I am curious to know if you 
> tested this yet? :)
>
> > If there is any way to sort other langague first than English, please
> > share with me.
>
> What's interesting here is, that we use libicu or libunistring for the 
> collation/sorting. Whether this works or not depends on a few things:
>
> 1. We need to fix our parser to allow the CASE/WHEN/END system. A quick 
> test here shows we don't allow that right now.
>
> 2. I don't actually know how SQLite would treat such a query on a 
> collated column, we would need to figure this part out.
>
> If those two steps work, Tracker should support it.

As precisely we have the collator taking care of sorting, I think
something like this should be implemented there, using CASE/THEN/END or
sqlite functions sound like ways to impersonate it.

An easy way to do this is to assign fixed weights to char ranges and
add/subtract to the collation return value before returning. Knowing
which locales might benefit of that could be more tricky... or maybe we
should just add a gsetting.

 Carlos

> --
>
> Can I ask how you're using tracker to understand why you need to sort 
> for different languages by query?
>
> Thanks,
>
> -- 
> Regards,
> Martyn
>
> Founder and CEO of Lanedo GmbH.
> _______________________________________________
> tracker-list mailing list
> tracker-list gnome org
> https://mail.gnome.org/mailman/listinfo/tracker-list