2009 is over. Yeah, sure, trueg, we know that, it has been
over for a while now! Ok, ok, I am a bit late, but still I
would like to get this one out - if only for my archive. So here
Let’s start with the major topic of 2009 (and also the beginning
of 2010): The new Nepomuk database backend: Virtuoso. Everybody who used Nepomuk had the
same problems: you either used the sesame2 backend which depends on Java and
steals all of your memory or you were stuck with Redland which had the
worst performance and missed some SPARQL features making important parts of
Nepomuk like queries unusable. So more than a year ago I had
the idea to use the one GPL’ed database server out there that
supported RDF in a professional manner: OpenLink’s
Virtuoso. It has all the features we need,
has a very good performance, and scales up to dimensions we will
probably never reach on the desktop (yeah, right, and 64k main
memory will be enough forever!). So very early I started
coding the necessary Soprano plugin which would talk to a locally
running Virtuoso server through ODBC. But since I ran into tons of small
problems (as always) and got sidetracked by other tasks I did not
finish it right away. OpenLink, however, was very interested in the
idea of their server being part of every KDE installation (why
wouldn’t they ;)). So they not only introduced a lite-mode which makes Virtuoso suitable
for the desktop but also helped in debugging all the problems that
I had left. Many test runs, patches, and a Virtuoso 5.0.12 release
later I could finally announce the Virtuoso
integration as usable.
Then end of last year I dropped the support for sesame2 and
redland. Virtuoso is now the only supported database backend. The
reason is simple: Virtuoso is way more powerful than the rest - not
only in terms of performance - and it is fully implemented in
C(++) without any traces of Java. Maybe even
more important is the integration of the full text index which
makes the previously used CLucene index unnecessary. Thus, we can
finally combine full text and graph queries in one SPARQL query.
This results in a cleaner API and way faster return of search
results since there is no need to combine the results from several
queries anymore. A direct result of that is the new Nepomuk Query API which I will discuss
So now the only thing I am waiting for is the first bugfix
release of Virtuoso 6, i.e. 6.0.1 which will fix the bugs that make
6.0.0 fail with Nepomuk. Should be out any day now. :)
The Nepomuk Query API
Querying data in
Nepomuk pre-KDE-4.4 could be done in one of two ways: 1. Use the
very limited capabilities of the ResourceManager to list resources with
certain properties or of a certain type; or 2. Write your own
SPARQL query using ugly QString::arg
With the introduction of Virtuoso and its awesome power we can
now do pretty much everything in one query. This allowed me to finally create a query API for KDE:
Nepomuk::Query::Query and friends. I won’t
go into much detail here since I did that before.
All in all you should remember one thing: whenever you think
about writing your own SPARQL query in a KDE application - have a
look at libnepomukquery. It is very likely that you can avoid the
hassle of debugging a query by using the query API.
The first nice effect of the new API (apart from me using it all
over the place obviously) is the new query interface in Dolphin.
Internally it simply combines a bunch of Nepomuk::Query::Term objects into a
Nepomuk::Query::AndTerm. All very readable
and no ugly query strings.
Dolphin Search Panel in KDE SC 4.4
Shared Desktop Ontologies
An important part of the Nepomuk
research project was the creation of a set of ontologies for describing desktop resources
and their metadata. After the Xesam
project under the umbrella of freedesktop.org had been convinced to use
RDF for describing file metadata they developed their own ontology.
Thanks to Evgeny (phreedom) Egorochkin and Antonie Mylka both the
Xesam ontology and the Nepomuk Information Elements Ontology were already
very close in design. Thus, it was relatively easy to merge the two
and be left with only one ontology to support. Since then not only
KDE but also Strigi and Tracker are using the Nepomuk ontologies.
At the Gran Canaria Desktop Summit I met some of the guys from
Tracker and we tried to come up with a plan to create a joint
project to maintain the ontologies. This got off to a rough start
as nobody really felt responsible. So I simply took the initiative
and released the shared-desktop-ontologies version 0.1 in
November 2009. The result was a s***-load of hate-mails and bug
reports due to me breaking KDE build. But in the end it was worth
it. Now the package is established and other projects can start to
pick it up to create data compatible to the Nepomuk system and
Today the ontologies (and the shared-desktop-ontologies package)
are maintained in the Oscaf project at Sourceforge. The situation
is far from perfect but it is a good start. If you need specific
properties in the ontologies or are thinking about creating one for
your own application - come and join us in the bug tracker…
Timeline KIO Slave
It was at the Akonadi meeting that Will Stephenson and myself
got into talking about mimicking some Zeitgeist functionality through Nepomuk.
Basically it meant gathering some data when opening and when saving
files. We quickly came up with a hacky patch for KIO and KFileDialog which covered most cases and
allowed us to track when a file was modified and by which
application. This little experiment did not leave that state though
(it will, however, this year) but another one did: Zeitgeist also
provides a fuse filesystem which allows to browse the files by
modification dates. Well, whatever fuse can do, KIO can do as well.
Introducing the timeline:/ KIO slave which
gives a calendar view onto your files.
Tips And Tricks
Well, I thought I would mention the Tips And Tricks section I wrote for the
techbase. It might not be a big deal but I
think it contains some valuable information in case you are using
Nepomuk as a developer.
Google Summer Of Code 2009
This time around I had the privilege to mentor two students in the Google Summer
of Code. Alessandro Sivieri and Adam Kidder did outstanding work on
Improved Virtual Folders and the Smart File Dialog.
Adam’s work lead me to some heavy improvements in the Nepomuk
KIO slaves myself which I only finished this week (more details on
that coming up). Alessandro continued his work on faceted file
browsing in KDE and created:
Alessandro is following up on his work to make faceted file
browsing a reality in 2010 (and KDE SC 4.5). Since it was too late
to get faceted browsing into KDE SC 4.4 he is working on Sembrowser, a stand-alone faceted file
browser which will be the grounds for experiments until the code is
merged into Dolphin.
Faceted Browsing in KDE with
In 2009 I organized the first Nepomuk workshop in Freiburg,
Germany. And also the second one. While I reported properly on the first one I
still owe a summary for the second one. I will get around to that -
sooner or later. ;)
Soprano gives us a nice command line tool to
create a C++ namespace from an ontology file: onto2vocabularyclass. It produces nice
convenience namespaces like Soprano::Vocabulary::NAO. Nepomuk adds
another tool named nepomuk-rcgen. Both were a bit clumsy to
use before. Now we have nice cmake macros which make it very simple
to use both.
See the techbase article on how to use the new
Without my knowledge (imagine that!) Andrew Lake created
an amazing new media player named Bangarang - a Jamaican word for noise,
chaos or disorder. This player is Nepomuk-enabled in the sense
that it has a media library which lets you browse your media files
based on the Nepomuk data. It remembers the number of times a song
or a video has been played and when it was played last. It allows
to add detail such as the TV series name, season, episode number,
or actors that are in the video - all through Nepomuk (I hope we
will soon get tvdb integration).
Edit metadata directly in Bangarang
Dolphin showing TV episode metadata
created by Bangarang
And of course searching for it works,
And it is pretty, too...
I am especially excited about this since finally applications
not written or mentored by me start contributing Nepomuk data.
Gran Canaria Desktop Summit
2009 was also the year of the first Gnome-KDE joint-conference.
Let me make a bulletin for completeness and refer to my previous blog post reporting on my
experiences on the island.
Well, that was by far not all I did in 2009 but I think I
covered most of the important topics. And after all it is ‘just a
blog entry’ - there is no need for completeness. Thanks for