A use-case for SPARQL and Nepomuk

As I got contacted by two different companies last few days who both had questions about integrating Tracker into their device, I started thinking that perhaps I should illustrate what Tracker can already do today.

I’m going to make a demo for the public transportation industry in combination with contacts and places of interest. Tracker’s ontologies cross many domains, of course (this is just an example).

I agree that in principle what I’m showing here isn’t rocket science. You can do this with almost any database technology. What is interesting is that as soon as many domains start sharing the ontology and store their data in a shared way, interesting queries and use-cases are made possible.

So let’s first insert a place of interest: the Pizza Hut in Nossegem

tracker-sparql -uq "
INSERT { _:1 a nco:PostalAddress ; nco:country 'Belgium';
               nco:streetAddress 'Weiveldlaan 259 Zaventem' ;
               nco:postalcode '1930' .
        _:2 a slo:Landmark; nie:title 'Pizza Hut Nossegem';
              slo:location [ a slo:GeoLocation;
                  slo:latitude '50.869949'; slo:longitude '4.490477';
                  slo:postalAddress _:1 ];
              slo:belongsToCategory slo:predefined-landmark-category-food-beverage  }"

And let’s add some busstops:

tracker-sparql -uq "
INSERT { _:1 a nco:PostalAddress ; nco:country 'Belgium';
               nco:streetAddress 'Leuvensesteenweg 544 Zaventem' ;
               nco:postalcode '1930' .
         _:2 a slo:Landmark; nie:title 'Busstop Sint-Martinusweg';
               slo:location [ a slo:GeoLocation;
                   slo:latitude '50.87523'; slo:longitude '4.49426';
                   slo:postalAddress _:1 ];
               slo:belongsToCategory slo:predefined-landmark-category-transport  }"
tracker-sparql -uq "
INSERT  { _:1 a nco:PostalAddress ; nco:country 'Belgium';
                nco:streetAddress 'Leuvensesteenweg 550 Zaventem' ;
                nco:postalcode '1930' .
          _:2 a slo:Landmark; nie:title 'Busstop Hoge-Wei';
                slo:location [ a slo:GeoLocation;
                    slo:latitude '50.875988'; slo:longitude '4.498208';
                    slo:postalAddress _:1 ];
                slo:belongsToCategory slo:predefined-landmark-category-transport  }"
tracker-sparql -uq "
INSERT  { _:1 a nco:PostalAddress ; nco:country 'Belgium';
                nco:streetAddress 'Guldensporenlei Turnhout' ;
                nco:postalcode '2300' .
          _:2 a slo:Landmark; nie:title 'Busstop Guldensporenlei';
                slo:location [ a slo:GeoLocation;
                    slo:latitude '51.325463'; slo:longitude '4.938047';
                    slo:postalAddress _:1 ];
                slo:belongsToCategory slo:predefined-landmark-category-transport  }"

Let’s now get all the busstops nearby the Pizza Hut in Nossegem:

tracker-sparql -q "
SELECT ?name ?lati ?long WHERE {
   ?p slo:belongsToCategory slo:predefined-landmark-category-food-beverage;
       slo:location [ slo:latitude ?plati; slo:longitude ?plong ] .
   ?b slo:belongsToCategory slo:predefined-landmark-category-transport ;
       slo:location [ slo:latitude ?lati; slo:longitude ?long ] ;
      nie:title ?name .
   FILTER (tracker:cartesian-distance (?lati, ?plati, ?long, ?plong) < 1000)
  Busstop Sint-Martinusweg, 50.87523, 4.49426
  Busstop Hoge-Wei, 50.875988, 4.498208

This of course was an example with only slo:Landmark. But that slo:location property can be placed on any nie:InformationElement. Meaning that for example a nco:PersonContact can also be involved in such a cartesian-distance query (which is of course just an example).

Let’s make an example use-case: We want contact details of friends (with publicized coordinates) who are nearby a slo:Landmark that is in a food and beverage landmark category, so that the messenger application can prepare a text message window where you’ll type that you want to get together to get lunch at the Pizza Hut.

Ok, so let’s add some nco:PersonContact to our SPARQL endpoint who are nearby the Pizza Hut:

tracker-sparql -uq "
INSERT { _:1 a nco:PersonContact ; nco:fullname 'John Carmack';
               slo:location [ a slo:GeoLocation;
                   slo:latitude '51.325413'; slo:longitude '4.938037' ];
               nco:hasEmailAddress [ a nco:EmailAddress;
                 nco:emailAddress 'john.carmack@somewhere.com'] }"
tracker-sparql -uq "
INSERT { _:1 a nco:PersonContact ; nco:fullname 'Greg Kroah-Hartman';
               slo:location [ a slo:GeoLocation;
                   slo:latitude '51.325453'; slo:longitude '4.938027' ];
               nco:hasEmailAddress [ a nco:EmailAddress;
                 nco:emailAddress 'greg.kroah@somewhere.com'] }"

And let’s add one person who isn’t nearby the Pizza Hut in Nossegem:

tracker-sparql -uq "
INSERT { _:1 a nco:PersonContact ; nco:fullname 'Jean Pierre';
               slo:location [ a slo:GeoLocation;
                   slo:latitude '50.718091'; slo:longitude '4.880134' ];
               nco:hasEmailAddress [ a nco:EmailAddress;
                 nco:emailAddress 'jean.pierre@somewhere.com'] }"

And now, the query:

tracker-sparql -q "
SELECT ?name ?email ?lati ?long WHERE {
   ?p slo:belongsToCategory slo:predefined-landmark-category-food-beverage;
       slo:location [ slo:latitude ?plati; slo:longitude ?plong ] ;
      nie:title ?pname .
   ?b a nco:PersonContact;
        slo:location [ slo:latitude ?lati; slo:longitude ?long ] ;
      nco:fullname ?name ; nco:hasEmailAddress [ nco:emailAddress ?email ].
   FILTER (tracker:cartesian-distance (?lati, ?plati, ?long, ?plong) < 10000)
  Greg Kroah-Hartman, greg.kroah@somewhere.com, 50.874715, 4.49158
  John Carmack, john.carmack@somewhere.com, 50.874715, 4.49154

These use-cases of course only illustrate the simplified location ontology in combination with the Nepomuk contacts ontology. There are many such domains in Nepomuk and when defining your own platform and/or a new domain on the desktop you can add (your own) ontologies. Mind that for the desktop you should preferably talk to Nepomuk first.

The strength of such a platform is also its weakness: if no information sources put their data into the SPARQL endpoint, no information sink can do queries that’ll yield meaningful results. You of course don’t have this problem in a contained environment where you define what does and what doesn’t get stored and where, like an embedded device.

A desktop like KDE or GNOME shouldn’t have this problem either, if only everybody would agree on the technology and share the ontologies. Which isn’t necessarily happening (fair point), although both KDE with Nepomuk-KDE and GNOME with Tracker share most of Nepomuk.

But indeed; if you don’t store anything in Tracker, it’s useless. That’s why Tracker comes with a file system miner and provides a framework for writing your own miners. The idea is that with time more and more applications will use Tracker, making it increasingly useful. Hopefully.



Today after I brought Tinne to the airport I drove around Zürichsee. She can’t stay in Switzerland the entire month; she has to go back to school on Monday.

While driving on the Seestrasse I started counting luxury cars. After I reached two for Lamborgini and three for Ferrari I started thinking: Zimmerberg Sihltal and Pfannenstiel must be expensive districts tooAnd yes, they are.

I was lucky today that it was nice weather. But wow, what a nice view on the mountain tops when you look south over Zürichsee. People from Zürich, you guys are so lucky! Such immense calming feeling the view gives me! For me, it beats sauna. And I’m a real sauna fan.

I’m thinking to check it out south of Zürich. But not the canton. I think the house prices are just exaggerated high in the canton of Zürich. I was thinking Sankt Gallen, Toggenburg. I’ve never been there; I’ll check it out tomorrow.

Hmmr, meteoswiss gives rain for tomorrow. Doesn’t matter.

Actually, when I came back from the airport the first thing I really did was fix coping with property changes in ontologies for Tracker. Yesterday it wasn’t my day, I think. I couldn’t find this damn problem in my code! And in the evening I lost three chess games in a row against Tinne. That’s really a bad score for me. Maybe after two weeks of playing chess almost every evening, she got better than me? Hmmrr, that’s a troubling idea.

Anyway, so when I got back from the airport I couldn’t resist beating the code problem that I didn’t find on Friday. I found it! It works!

I guess I’m both a dreamer and a realist programmer. But don’t tell my customers that I’m such a dreamer.

Bern, an idyllic capital city

Today Tinne and I visited Switzerland’s capital, Bern.

We were really surprised; we’d never imagined that a capital city could offer so much peace and calm. It felt good to be there.

The fountains, the old houses, the river and the snowy mountain peaks give the city an idyllic image.

Standing on the bridge, you see the roofs of all these lovely small houses.

The bear is the symbol of Bern. Near the House of Parliament there was this statue of a bear. Tinne just couldn’t resist to give it a hug. Bern has also got real bears. Unfortunately, Tinne was not allowed to cuddle those bears.

The House of Parliament is a truly impressive building. It looks over the snowy mountains, its people and its treasury, the National Bank of Switzerland.

As you can imagine, the National Bank building is a master piece as well. And even more impressive; it issues a world leading currency.

On the market square in Oerlikon we first saw this chess board on the street; black and white stones and giant chess pieces. In Bern there was also a giant chess board in the backyard of the House of Parliament. Tinne couldn’t resist to challenge me for a game of chess. (*edit*, Armin noted in a comment that the initial position of knight and bishop are swapped. And OMG, he’s right!)

And she won!

At the House of Parliament you get a stunning, idyllic view on the mountains of Switzerland.


Last few weeks I have been working on the new thumbnail infrastructure for future Maemo products.

Last year I made a specification for requesting thumbnails over D-Bus. Afterward I made a quick prototype and replaced the hildon-thumbnailer library of Maemo with it. This prototype will be deployed on the standard N900 image. It’s too late to replace Fremantle’s thumbnailer with the new stuff. It takes time to properly test it.

While I was developing both the specification and the prototype XFCE developer Jannis Pohlmann contacted me about rewriting my prototype for use in the XFCE project. Tumbler was born.

The nice people at Nokia are more interested in working with upstream projects instead of maintaining own products separately, so I shifted my focus from hildon-thumbnail to contributing to Jannis’ Tumbler project.

We realized that we needed different kinds of schedulers so while Jannis was developing Tumbler I kindly asked to consider abstracting scheduling a bit. Tumbler now has two schedulers. The background one sets I/O and scheduler priorities to IDLE and processes its thumbnail tasks in FIFO order. The foreground uses LIFO and will instead of grouping Ready signals together, emit them immediately after each single thumbnail is finished. Default is of course foreground.

We also realized that thumbnail flavors are going to be platform specific. So we added some support for this in the DBus APIs that we further fine tuned and versioned.

Congratulations and appreciation to Jannis who made Tumbler’s code and design really nice. Also thanks a lot for constructively considering our requirements and helping adapting Tumbler’s code to cope with them.

I know you for example worked one long night on this stuff, so I officially owe you a few beers and/or cocktails next conference.

How about FOSDEM?



In a discussion some concluded that technology X is ‘more tied to GNOME’ than technology Y because ‘more [GNOME] people are helped by X’ due to dependencies for Y. Dependencies that might be unacceptable for some people.

This smells like utilitarianism and therefore it’s subject to criticism.

Utilitarianism is probably best described by Jeremy Bentham as:

Ethics at large may be defined, the art of directing men’s actions to the production of the greatest possible quantity of happiness.

— Bentham, Introduction to the Principles of Morals and Legislation

A situational example that, in my opinion, falsifies this:

You are standing near the handle of a railroad switch. Six people are attached to the rails. Five of them at one side of the switch, one at the other side of the switch. Currently the handle is set in such a way that five people will be killed. A train is coming. There’s no time to get help.

  • Is it immoral to use the handle and kill one person but save five others?
  • Is it immoral not to use the handle and let five people get killed?

The utilitarianist chooses the first option, right? He must direct his actions to the production of the greatest possible quantity of happiness.

Body of the discussion

Now imagine that you have to throw a person on the rails to save the lives of five others. The person would instantly get killed but the five others would be saved by you sacrificing one other.

A true utilitarianist would pick the first option in both exercises; he would use the handle and he would throw a person on the rails. In both cases he believes his total value of produced happiness is (+3) and he believes that in both situations picking the second option means his total value of produced happiness is (-4) + (+1) = (-3). The person who picks the second option is therefore considered ethically immoral by a true utilitarianist.

For most people that’s not what they meant the first time. Apparently ethics don’t allow you to always say (+4) + (-1) = (+3) about happiness. I’ll explain.

The essence of the discussion

Psychologically, less people will believe that throwing a person on the rails is morally the right thing to do. When we can impersonificate we make it more easy for our brains to handle such a decision. Ethically and morally the situation is the same. People feel filthy when they need to physically touch a person in a way that’ll get him killed. A handle makes it more easy to kill him.

Let’s get back to the Gnome technology discussion … If you consider pure utilitarianism as most ethical, then you should immediately stop developing for GNOME and start working at Microsoft: writing good Windows software at Microsoft would produce a greater possible quantity of happiness.

Please also consider reading criticism and defence of utilitarianism at wikipedia. Wikipedia is not necessarily a good source, but do click on some links on the page and you’ll find some reliable information.

Some scientists claim that we have a moral instinct, which is apparently programmed by our genes into our brains. I too believe that genetics probably explain why we have a moral system.

The developer of X built his case as following: My technology only promotes happiness. The technology doesn’t promote unhappiness.

It was a good attempt but there are multiple fallacies in his defense.

Firstly, in a similar way doesn’t technology Y promote unhappiness either. If this is assumed about X, neither promote unhappiness.

Secondly, how does the developer of X know that his technology promotes no unhappiness at all? Y also promotes some unhappiness and I don’t have to claim that it doesn’t. That’s a silly assumption.

Thirdly, let’s learn by example: downplaying the amount of unhappiness happens to be the exact same thing regimes having control over their media also did whenever they executed military action. The act of downplaying the amount of unhappiness should create a reason for the spectator to question it.

Finally, my opinion is that the very act of claiming that ‘X is more tied to GNOME’, will create unhappiness among the supporters of Y. Making the railroad example applicable anyway.

My conclusion and the reason for writing this

‘More’ and ‘less’ happiness doesn’t mean a lot if both are incommensurable. Valuations like “more tied to GNOME” and “less tied to GNOME” aren’t meaningful to me. That’s because I’m not a utilitarianist. I even believe that pure utilitarianism is dangerous for our species.

To conclude I think we should prevent that the GNOME philosophy is damaged by too much utilitarianism.

Moral indulgence

In the last few days people seemingly implying a descent from superiority of moral highground to me, have called upon me (in private conversations) to decide for my readers if the content that I write is morally acceptable for planet.gnome.org. Their reasoning is that I should feel an implied responsibility for the content of that website.

If I don’t take the responsibility that readers have themselves already, I’m to be considered a coward. That’s because, according to these people, I avoid the moral responsibility to uphold an imaginary highground reputation of the organization behind said website.

It needs no illustration that this is just the opinion of a group within the GNOME community. Not the entire community. Nonetheless this seemingly moral superiority is not to be mistaken with a condescending circus show.

The moral of respect for other opinions is a meme that for the last decades (and I hope in future too) has been a very successful one. I consider this meme to be the most important one humanity ever got convinced of.

Moral superiors do not need to present empirical proof of correctness in their Sophia. The truth of their moral values are unquestionable.

Let’s assume this to be the case: it’s immoral to only assume that your readers will make up their own minds about ideas that appear on websites like planet.gnome.org. Instead, it’s a necessity that each and every author of a blog, from which planet.gnome.org pulls content, is required to have a “responsibility of content”.

I conclude that it isn’t necessary that the audience of that website gets an honest illustration of who we are: human beings who are sometimes geniuses and sometimes idiots.

Instead it’s necessary that we are portrayed as good role models. Concepts such as good and bad are of course defined by the superiors. Those concepts are unquestionable.

Let me be clear that I disagree with this.

I questioned whether only intent can either be good or bad, but that question was refuted as irrelevant. For it’s the beholder who matters. Not the producer.

The reason for this irrelevance being that an audience doesn’t take the responsibility of trying to understand intent. I disagree with this conclusion. I think the audience does understand intent.

I have decided to tag my future posts as “condescending” in case I feel the content might be interpreted as showing superiority. Don’t be surprised if the majority of posts will be tagged as such.

The freedom to choose is morally more important to me than the necessity to mark responsible content. Therefore I ask my audience, and planet maintainers, to decide for themselves.

Mindstorm … s

You buy a bunch of Lego Mindstorms bricks and you start building a robot to remotely control your mobile devices.

Well, that’s the official explanation.

The actual explanation is that this is what happens when you are 26 years of age, your girlfriend tells you you are almost 30 and that when you are 30 it’s the end of your youth (although, people of that age usually tell me this ain’t true), you are a nerd of the type software developer (and quite addicted to this too), you have your own business and therefore your accountant asks to make some expenses (like .. buying a Mindstorms robot! No?).

I acknowledge it’s probably just an early midlife crisis. Boys want to make things, fiddle with stuff, put things together. Whereas girls, girls just wanna have fun. I’m totally guilty of being a boy. I know. (although, I’m sure a lot of girls enjoy making things too — before I get killed by a group of feminists –).

Now that the model itself is finished, I clearly see what I am becoming: an old lonely dude who plays with trains, electricity stuff and mostly breaks things just to put them back together. I’ll probably die getting electrocuted while trying to take apart a by that time old holographic 3D gesture recognizing display, as I’m trying to figure out whether some evil corporation is spying on its customers by using such electronic devices.

But, isn’t that cute? No? I mean, Tinne, seriously, now I must be ‘like’ a younger dude, no? I have been playing with toys for kids aged 11 to 16 (that’s what the Lego box’s age indicator says, so it must be true). Anyway, the only way that it can get worse now, is if I’ll start writing software for this Lego model. I’ll have a camera view on my screen where I can mouse-over so that the robot will follow my mouse pointer. With a library like GStreamer I can let that camera image go efficiently over a distance. Sending some commands over a socket ain’t very hard.

About the bot itself: it has three axis. One (the X one) uses normal wheels, two others (Y and Z) are built on top of the chassis. All axis are controlled by Mindstorms motors. The Mindstorms computer thing is integrated in the model, there’s a touch sensor on one of the axis (the Z one). I don’t yet have this software, that’s the next thing I’ll (try to) finish. I’ve spend ~ 450 euros on this thing (the normal Mindstorms package didn’t have enough bricks, but the programmable thing, the sensors and the motors are ~ 300 euros).

But hey, 450 euros for something that you could give to a little fellow as soon as you are done playing with it? That’s not much for multi functional and multi age toys! I mean, if I get bored of this thing, I can make another robot with it. If you have a son (or a technical minded daughter), you can let him (or her) play with the Lego bricks while watching his (her) brains grow! You can’t convince me that today’s computer games are better for training a kid’s brain than Lego.

After the kid is finished building the bot, you can make the software for it. Hah! Perfect father – son (or daughter) relationship. You actually help him make his toys, and you enjoy doing that! And … he’ll get interested in software development, join one of the many free software communities, he’ll find a job in IT as programmer, etc etc.

Lego rocks!