Permission to break feature freeze for Nepomuk and Soprano

Richard Dale Richard_Dale at
Mon Sep 3 18:08:08 BST 2007

On Monday 03 September 2007, Evgeny Egorochkin wrote:
> On Monday 03 September 2007 18:53:27 Richard Dale wrote:
> > On Monday 03 September 2007, Sebastian TrĂ¼g wrote:
> > > Hi guys,
> > >
> > > there has been a long silence around Nepomuk. Well, the main reason is
> > > that I was working heaviliy on Soprano2 [1]. It comes with a bunch of
> > > new features, a much cleaner API, a server/client architecture (quite
> > > simple but waaaay faster than DBus), and I intend to replace the
> > > Nepomuk middleware with it. I already did it locally and a commit
> > > "should" not break anything once Soprano2 is copied to kdesupport.
> > >
> > > The main advantage of all this is: speed. No more DBus for requesting
> > > data. It is now done via tcp (and I would love some tips and help to
> > > add support for unix socket communication)
> > >
> > > If there are no objections until this evening I will proceed (I know it
> > > is short notice but I don't think it is such a big deal yet.)
> > >
> > > Cheers,
> > > Sebastian
> > >
> > > [1] branches/work/sorano2
> >
> > I don't know about speed, but from what I've seen of the SPARQL query api
> > it only returns results as C++ over dbus (as a
> > Nepomuk::RDF::QueryResultTable). The query itself is a text string which
> > is language independent and fine. So the results are retrieved as xml
> > text, marshalled to c++, then marshalled to the dbus wire format. At the
> > other end, the are put back into the original c++ classes. In ruby there
> > would be a further step where those c++ instances would be wrapped with
> > Ruby classes.
> >
> > What I would prefer is that the query results are sent as a an xml
> > string 'application/sparql-results+xml' over dbus and then the client can
> > choose what it wants to do with it, depending on what language the client
> > is written in. For instance, a C++ client could convert the xml to
> > Nepomuk::RDF::QueryResultTable, or a ruby client could convert to the
> > ActiveRDF result format. Maybe there is a problem because Nepomuk needs
> > to return quads when named graphs are used, instead of just triples - I'm
> > not enough of an expert to know if using sparql/xml for the result sets
> > would cause problems with that.
> You underestimate the performance overhead of conversions to and from XML +
> DBUS overhead. In certain cases like PIM using nepomuk with all this
> overhead would be as sane as accessing the filesystem via DBUS and XML.
> Retrieving metadata for a single file is not a problem with either
> approaches, but in heavy-load conditions it can be(and if there aren't any
> heavy usage scenarios, why bother with unneded stuff at all?)
> How significant performance penalty we are talking about? I didn't do
> benchmarks. Sebastian says it makes a big difference. So far I personally
> don't have any reason not to trust him on this.
> Still would be nice to see the actual numbers.
Yes, without measurements I don't have much of an opinion.

> > I am keen to be able to use jabber XMPP as a transport for peer to peer
> > SPARQL queries between KDE users if they wanted to exchange their own
> > meta-data in their local triple stores, such as restaurant
> > recommendations or whatever. So I think Nepomuk should be as transport
> > and language independent as possible, and using xml as the result set
> > format makes that easier.
> A valid point. Quite likely dropping the XML interface completely is not
> ok, but making it the primary one seems too unrealistic.
Yes, I agree - I'll be happy as long as we can have both, and it will be 
easier to interact with non-c++ clients.

> The most typical and performance-demanding use case will be c++ client
> interacting with nepomuk with native interface and tcp link will likely
> greatly improve this. It's easy to add a XML serialization on top of c++
> classes if anyone needs it.
> As to RDF backend already returning RDF/XML, it's not necessarily so.
> -- Evgeny

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