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Wikidata on the Moon

29 June 2015


I recently posted updates Wikidata world maps that show the distribution of the contents of Wikidata on Earth. The maps also show where the specific interests of several language editions of Wikipedia are. Emilio J. Rodríguez-Posada suggested to do the same for the Moon. Here are the results.

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Knowledge Graphs JWS special issue

Oct 1 2014


The Journal of Web Semantics invites submissions to a special issue on Knowledge Graphs to be edited by Markus Krötzsch and Gerhard Weikum. Submissions are due by 31 March 2015 (extended from 28 February 2015).

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How to install (K)Ubuntu 14.04 on Macbook 7,1

2 Aug 2014


I have just re-installed Kubuntu 14.04 64bit from scratch on my Macbook Pro 7,1 (2010). This was surprisingly hard, given that I had been running the exact same system in 32bit mode before. Moreover, it turns out that the problems are not at all related to 64bit vs. 32bit (or to Kubuntu vs. Ubuntu) but to seemingly unimportant details of how you install. It took me almost two days to figure this out, so here is my quick installation guide. Read more …

Kubuntu screen setup emergency guide

May 16 2014


You are giving a talk in 5 min. You attach your Kubuntu 14.04 LTS "Trusty Thar" laptop to the beamer. The laptop screen goes black for a second ... reappears ... and ... nothing. The beamer reports "no input". No message on your screen. 4min to go. Panic.

Keep cool. Do not reboot. Do not turn off the beamer. Both take too long and never fixed anything for me that was not fixed otherwise. Try the quick things first:

Emergency Routine 1

  • Press ALT+F2 (This opens the KDE quick starter. If not on KDE, open some other terminal input window.)
  • Type xrandr --auto and press return.
With some luck, you can do this even if all screens are black. Still nothing? Read more …

Sex Distributions in Research

Oct 13 2013


Gender imbalance in academia is a huge topic these days, especially in the STEM fields. Computer Science, with its close connection to tech/Web/geek culture is buzzing with all kinds of related activities, funding programs, and (sometimes heated) debates. The statistics we get to see in these discussions are often very coarse, talking about all of Computer Science. Researchers thus tend to get the impression that their own (specific) field is merely suffering from wider issues beyond their control. So I was wondering how strong is gender imbalance in (really) specific research fields? Considering the conferences I go to, I can certainly say that some are more balanced than others. For journals, I have no idea. So I did a little data mining over the weekend to find out, using DBLP and Wikidata as main data sources.Read more …

How to Extract Used Entries From BibTeX Files

Apr 21 2012


When using BibTeX to create bibliographies with LaTeX, it is convenient to work with one large bib file that defines all relevant references, and that is re-used again and again in new LaTeX projects. Sometimes, however, such a large file is unwieldy, and you want to create a smaller file that contains only the entries that you have actually used in a document. I am hereby releasing a powerful software suite for solving this problem: BibDigest. Read more …

Wikidata to Bring Semantic Data to Wikipedia

Mar 30 2012


The Wikidata project – a major effort to establish a platform for editing and sharing data among all Wikipedia communities – will start next Monday, 2 April 2012, and we are already very busy drawing diagrams and discussing data semantics here in Berlin (I have the pleasure of being the Data Architect of the project, so I better get cracking to define some data model).

Today, Wikimedia Germany e.V. has also published there first official press release about the project, entitled Data Revolution for Wikipedia, and what an echo we get! The Techcrunch article is quite nice; the Twitter feedback on #wikidata is beyond my capacity. Now all that remains to be done is to actually implement it …

Technical details will be published on pretty much immediately. We will need strong support from the Semantic Web community to leverage this data. From the discussions we are having, it will be quite rich and more than your average RDF. Certainly some technical and academic challenges to be addressed there.

PODS'12 Going (Semantic) Web

Jun 28 2011


Next year's PODS 2012, the 31st edition of the established SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems, is going to have a special call for "emerging database environments and applications" which happens to be very much geared to Semantic Web/Web of Data technologies. This would be a great chance to get some of the database/data mining/query-related work that is happening around semantic technologies to receive more visibility and appreciation in the database community.

The call for papers is found below. As you can see, more than one of the special areas could fit to (Semantic) Web-related work. Abstract submission is on November 20, so plenty of time to get ready :-) View call for papers …

The State of the UNION: Why no SPARQL Condition Should be Second Class

28 Apr 2011


While implementing RDF-based query answering for Semantic MediaWiki (SMW), I realized that the popular SPARQL query language for RDF has what I consider to be a major design flaw. Admittedly, I had been slightly too optimistic: surely, moving from SQL to SPARQL would be a piece of cake! Have we not had exactly the same RDF-ish data model in mind when designing SMW? And is SMW not a natural friend to all of its fellow Semantic Web technologies? Well, let's just say that the friendship has cooled down a bit in certain matters …Read more …

Ending a Difficult Relationship

Mar 13 2011


Dear MacOS,

the past seven months with you as my single OS were an experience that I don't want to miss, but we just cannot go on like this. I'm exhausted by our quarrels about which window is in front. You wanted to lock me in, but I just felt locked out. I needed my freedom, you just gave me embedded X servers and virtual machines. Don't pretend to be surprised, I know why you wanted to prevent me from shrinking your partition! But your intrigues were in vain, and I have now returned to my first love, Kubuntu. Maybe we can see each other again from time to time. I still love your body, and Kubuntu is completely okay with this, as long as we don't multitouch. Farewell Snow Leopard! No more Cmd+Q disasters, no more "each tool has a different use for the home key" hassles, no more weekly updates for an iTunes I never use!


P.S. You still had all my emails, although you could never find them with your Spotlight. I moved them to my new home this morning while you were sleeping.


Moving from Linux to Mac

Aug 19 2010. I have recently moved from Linux to Mac, with all the advantages and disadvantages involved. In the process, I logged my customisation steps to create a Mac OS Installation Guide for Linux Users that can probably also be useful to other Linux users.


How to migrate emails from Linux to Mac

Aug 6 2010. I recently had to figure out how to migrate emails from KMail to Mac. Hopefully, my description can be of some use to others who move away from KMail for whatever reason. The basic method should work for moving KMail emails to virtually any other email client, and it can be used even if you cannot run KMail any more (as was the case for me since my Linux laptop passed away one morning without warning).


OWL 2 and how to cite it

Oct 27 2009. It's done! The OWL 2 Web Ontology Language is a W3C Recommendation. Many OWL tools are already compatible with the new specs, and it is expected that all are transitioning to the newer version. OWL 2 consists of many (13) documents, but it has a short overview document and an extended Primer as entry points.

Thus, only one question is left open: how should you cite the new standard? I recommend the following bibtex entries for the aforementioned references:

 author    = {W3C {OWL Working Group}},
 title     = {{OWL~2 Web Ontology Language: Document Overview}},
 publisher = {W3C Recommendation},
 note      = {Available at \url{}},
 year      = {27 October 2009}

 editor    = {Pascal Hitzler and Markus Kr\"{o}tzsch and Bijan Parsia and
              Peter F. Patel-Schneider and Sebastian Rudolph},
 title     = {{OWL~2 Web Ontology Language: Primer}},
 publisher = {W3C Recommendation},
 note      = {Available at \url{}},
 year      = {27 October 2009}

Yes, using @book is a good idea here: bibtex recommends picking reference types by appearance, not by name (and there is no @w3cstandard anyway). The other documents can be cited like the Primer (I just use author for the overview since editor would look inappropriate at this place).

Of course you could also cite a textbook on OWL 2 ;-)


HTML5, RDFa, fights about web semantics

Jul 8 2009. The recent events in the ongoing HTML5 vs. XHTML war, quite unfortunately, are utilised by some to restart a battle of RDFa vs. microformats that appears to be rather pointless. Read more …

Theory or Research?

May 5 2009. When doing a review for an IEEE journal, I have been asked to respond to the following question:

Review classicifation.png

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Spam without purpose

15 Dec 2008. A spam mail I just received asks me to buy an oil tanker (7,000dwt). Apparently, I am not the first to get such offers. The obvious question is: why? (I note that there is no attachement, no suspicious or different HTML component, not even links to browse to). So here are some hypotheses.Read more …

Call for tourists

Sep 17 2008. For making a scientific conference a success, it is of course important to phrase the call for papers in a way that attracts contributions. So what should be written in the first paragraph? Read more …

Hard wear

Sep 3 2008. Riding a caster board is a great way of getting to work. It is still important to wear protective gear. In my case, this was my rucksack, filled with a Thinkpad T41p as an additional shock absorber. It still works, though the screen dangles a little on the side where the metal joint has burst. But sitting crouched in front of this laptop for years, my spine had already suffered enough – it was about time for the machine to give something back!

How I changed the world

Aug 25 2008. Of course, we all want to change the world, don't we? But in the age of the Web, we may often do so without actually noticing. Quite incidentally, I found out yesterday that I have contributed to possibly thousands of web pages. My contribution is the following:

Sort none.gif

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Semantic MediaWiki 1.2: bringing OWL to the Web

Jul 11 2008. After a lot of work it finally done: version 1.2 of Semantic MediaWiki has been released and is available for download. The new release does of course include many new features, but it also has some interesting additions regarding proper Semantic Web technologies. Read more …

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