Re: [Tracker] Result of GetMetadata DBUS Method

[Adrien Bustany <abustany gnome org>]

Le Sat, 24 Sep 2011 18:50:06 -0400,
Nikolaus Rath <Nikolaus rath org> a écrit :

> Adrien Bustany <abustany-rDKQcyrBJuzYtjvyW6yDsg public gmane org>
> writes:
> > > > > In tracker 0.8.17, an example result of the GetMetadata DBUS
> > > > > method is
> > > > >
> > > > >  a nfo:PaginatedTextDocument ;
> > > > >         nie:title "SV Meldung" ;
> > > > >         nco:creator [ a nco:Contact ;
> > > > >         nco:fullname "nikratio"] ;
> > > > >         nie:contentCreated "2011-08-10T20:12:38Z" ;
> > > > >         nao:hasTag [ a nao:Tag ;
> > > > >         nao:prefLabel "()"] ;
> > > > >         dc:format "application/pdf" ;
> > > > >         nie:description "()" ;
> > > > >         nfo:pageCount 1 ;
> > > > >         nie:plainTextContent "blablabla" .
> > > > >
> > > > > With tracker 0.10.21, however, the same document now gives
> > > > >
> > > > >  a nfo:PaginatedTextDocument ;
> > > > >         nie:title "SV Meldung" ;
> > > > >         nco:creator [ a nco:Contact ;
> > > > >         nco:fullname "nikratio"] ;
> > > > >         nie:contentCreated "2011-08-10T20:12:38Z" ;
> > > > >         dc:format "application/pdf" ;
> > > > >         nie:description "()" ;
> > > > >         nao:hasTag ?tag1 ;
> > > > >         nfo:pageCount 1 ;
> > > > >         nie:plainTextContent "blablabla" .
> > > > > } } WHERE { {
> > > > > ?tag1 a nao:Tag ; nao:prefLabel "()" .
> > > > >
> > > > >
> > > > > I don't know enough about the syntax used here, so I won't claim
> > > > > that it's wrong. However, rdflib fails to parse this and thus
> > > > > breaks my application.
> > > > >
> > > > > Can someone tell me if this is a bug in tracker or in rdflib?
> > > >
> > > > Could you share the error message that rdflib gives you?
> > >
> > > Sure, it's at http://code.google.com/p/rdflib/issues/detail?id=190
> >
> > Most likely rdflib doesn't like the fact that the WHERE of the
> > INSERT is not closed?
>
> rdflib actually tries to parse this as Turtle RDF. But unless I'm
> reading the specs wrong, Turtle does not have a WHERE, so am I right
> to assume that GetMetadata has been changed to no longer return valid
> Turtle RDF, but partial SPARQL statements?
>
> If so, this makes it very hard to use GetMetadata() for anything else
> but tracker. Is there any way to get something that's easier to parse
> from tracker-extract?
>
>
> Thanks,
>
>    -Nikolaus

Well, tracker-extract actually *never* returned turtle, at least as far
as I know (now, I'm not completely familiar with that component). I
guess the fact that previous versions returned SPARQL that looked like
turtle is at most a coincidence :) (note: turtle does not have INSERT
either). GetMetadata being an internal API call, it's not exactly
meant to be easy to use for 3rd party apps, and it's actually tied
quite tightly with the SPARQL the the FS miner generates. I'm not sure
of what would be the easiest way for you to use that API now :/ Getting
the complete SPARQL and inserting it into an in-memory db (for example
Sesame) before querying it would be an option, but that really sounds
complex and sub-optimal... A simpler option would be to apply a few
transformations to the SPARQL to make it look like turtle again, but
that does not sounds like a bullet proof solution.

Cheers

Adrien