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Python introduction movie

I just wanted to share this movie about the Python programming language. Although it’s a bit dated, I feel the movie still provides a nice overview of the benefits of Python, and explains why the language is good for educational purposes. It can be found at

You’ll see interviews with Guido van Rossum (creator of the Python language), Eric S. Raymond (author of “The Cathedral and the Bazaar” and the excellent article “Why Python?”), and Tim Peters (known a.o. from The Zen of Python).

The film was originally called “A Python Love Story”, and was was made in 2001 by a class of high school students in Yorktown High School (Arlington, Virginia) together with their Computer Science teacher Jeff Elkner. Elkner is known for translating Allen Downey‘s “How to Think Like a Computer Scientist” into Python. The original (and longer) version of the video is available from the Python Bibliotheca.

Research update

Quite a few things happened since I last posted about my research. Here is a (not so short) summary of what happened during my blogging leave of absence

Ubicomp 2009

Our work on supporting why and why not questions to improve end-user understanding in Ubicomp environments was accepted as a poster to Ubicomp 2009

Answering Why and Why Not Questions in Ubiquitous Computing

Jo Vermeulen, Geert Vanderhulst, Kris Luyten, and Karin Coninx. Answering Why and Why Not Questions in Ubiquitous Computing. To appear in the Ubicomp ’09 Conference Supplement (Poster), Orlando, Florida, US, September 30th – October 3rd, 2009, 3 pages.

Abstract: Users often find it hard to understand and control the behavior of a Ubicomp system. This can lead to loss of user trust, which may hamper the acceptance of these systems. We are extending an existing Ubicomp framework to allow users to pose why and why not questions about its behavior. Initial experiments suggest that these questions are easy to use and could help users in understanding how Ubicomp systems work.

There is a separate page for the poster on my homepage, including a PDF version of the poster and the extended abstract.

Mario Romero has an excellent Ubicomp 2009 photo set on Flickr.

Here’s a picture of me explaining the poster:


And here I am presenting in the One Minute Madness session:



Karel Robert helped me create a video for the One Minute Madness session that would stand out. Although it might have been a bit too attention-grabbing, I certainly had fun making it and presenting in the Madness session.

Here is the video:

Next to presenting my poster, I also served as a Ubicomp 2009 student volunteer, which earned me a place in Joe McCarthy’s opening slides for the conference (slide 6)

Being a student volunteer was lots of fun! I got to meet a lot of interesting people, and still had the opportunity to follow most of the sessions. I also explored the parks together with a few of the other volunteers (Ubicomp 2009 was held in Disney World), and we even played beach volley on the last day

When we went to the Magic Kingdom, I had to see Randy Pausch’s plaque at the Mad Tea Party:

Randy Pausch plaque in Disney World containing a quote from the Last Lecture

The plaque contains a quote from Randy’s Last Lecture:

Randy Pausch: Be good at something; It makes you valuable... Have something to bring to the table, because that will make you more welcome.

If you haven’t watched the Last Lecture yet, I strongly recommend you do! It will be an hour well-spent.

Full paper accepted to AmI 2009

The full paper that we submitted to the third international conference on Ambient Intelligence 2009, was accepted as well. This work was a collaboration with Jonathan Slenders, one of our Master’s students.

I Bet You Look Good on the Wall: Making the Invisible Computer Visible

Jo Vermeulen, Jonathan Slenders, Kris Luyten, and Karin Coninx. To appear in the Proceedings of AmI ’09, the Third European Conference on Ambient Intelligence, Salzburg, Austria, November 18th – 21st, 2009, Springer LNCS, 10 pages.

Abstract: The design ideal of the invisible computer, prevalent in the vision of ambient intelligence (AmI), has led to a number of interaction challenges. The complex nature of AmI environments together with limited feedback and insufficient means to override the system can result in users who feel frustrated and out of control. In this paper, we explore the potential of visualizing the system state to improve user understanding. We use projectors to overlay the environment with a graphical representation that connects sensors and devices with the actions they trigger and the effects those actions produce. We also provided users with a simple voice-controlled command to cancel the last action. A small first-use study suggested that our technique could indeed improve understanding and support users in forming a reliable mental model..

There is again a separate page for the paper on my homepage, together with a PDF version.

Basically, our technique visualizes the different events that occur in a Ubicomp environment, and shows how these events can lead to the system taking actions on behalf of the user and what effects these actions have. Here is a video of the technique:

The AmI 2009 conference takes place in Salzburg in about three weeks.

Talk at

I also submitted a paper to‘s (the Belgian SIGCHI chapter) 2009 Fall Conference on New Communities. The paper was titled Improving Intelligibility and Control in Ubicomp Environments, and motivated the need for intelligibility and control in Ubicomp while also giving a short summary of the Ubicomp 2009 poster and AmI 2009 paper.

Here are the slides:

[slideshare id=2276932&doc=sigchibe-091019085111-phpapp02]

Thanks to everyone at our lab who contributed in one way or another (either by participating in user studies, or by reviewing drafts of the papers)

Specials thanks to:

  • Karel Robert for designing the visualizations we used in the AmI 2009 paper and for helping me with the Ubicomp 2009 One Minute Madness video.
  • Daniël Teunkens for drawing the why question storyboards that were used in the presentation.
  • Mieke Haesen for being a great actress in the AmI 2009 movie
  • Kris Gabriëls for posing in the picture we used for the Ubicomp 2009 poster abstract.

Facade update: code available and information about related student projects

My previous posts on face detection with Python and on changing the user’s presence when he/she is detected by the webcam are two of the most popular articles on my blog. There were quite a few comments that asked about the code for this project.

Although I already created a Facade project page a while ago and made the code available through Bazaar, I never announced it here. To make it easier to try the script out, I also uploaded an archive of the code. This version includes a simple Python script that works on Windows ( that performs face detection.

I noticed today that Jinwei Gu, a PhD student at the University of Columbia and teaching assistant for the course COMS W4737 (E6737) Biometrics, included my blog post in a list of links to resources for doing face detection.

Last year, two students improved the presence detection in Facade during their Bachelor’s theses.

Bram Bonné worked on the network aspect, to allow users to have their presence detected on multiple computers. When users would move from one computer to another (or to a mobile device), their messages would automatically be routed to their current machine.

Here are a few screenshots from Bram’s thesis:

Multi-device presence

An everywhere messaging service that takes into account the user's presence.

Bram also created a demo video of his system:

Kristof Bamps worked on supporting a more diverse set of sensors (e.g. presence of a Bluetooth phone, keyboard and mouse input). He used a decision tree to model all these sensors, and determine the user’s correct presence based on the collected information.

Two screenshots from Kristof’s thesis:

Showing the user's presence state

A history of presence changes

Kristof’s demo video:

I have unfortunately not yet found the time yet to merge Kristof’s and Bram’s code into the main Facade branch, but this should not be too big of a problem.


Apparantely, there’s a Communications of the ACM group blog now, called blog@CACM. There is also a blog roll that includes the blog of Daniel Lemire, which happens to be one of my favorite research blogs. Although Daniel works in a different subdiscipline of computer science, I enjoy reading his research advice and interesting viewpoints on the process of doing research.

The group blog features an interesting post by Tessa Lau, titled Three Misconceptions About Human-Computer Interaction, which raises a few interesting points. In my opinion, HCI is much more fundamental to creating interactive systems than people usually believe. In this context, I would like to refer to an interview with Patrick Baudisch that I recently read, in which he explains how he got started in HCI:

Doantam: How did you get started working on human-computer interaction?

Patrick: Without knowing it. I was a Ph.D. student in Darmstadt, Germany and worked on user interfaces for information filtering systems. A friend of mine saw my work and said “oh, I did not know you were in HCI, too”.

That was the first time I heard of that field.

New Homepage

I finally updated my homepage today. It used to be a custom Rails website, with RHTML views that I edited through SSH. I never got around to create a database model for my website, and to be frank, I am glad that I didn’t since my homepage’s structure changed a lot. On the other hand, having to login remotely and edit the view with Vim every time I wanted to add a publication to my homepage was too big of a burden. The net result was that I did not update my website as much as I wanted to.

A few months ago I decided to look for a better solution. I experimented with various solutions, including Drupal (with a lot of help from Wim Leers, thanks Wim!) and WikkaWiki (with a few tips from Dario Tarborelli) before finally settling on PmWiki. In this post, I will describe my rationale for choosing PmWiki over Drupal and WikkaWiki.

An advantage of Drupal is that it is extremely flexible. For instance, the website’s menu and corresponding URL structure can be completely customized. It also allows you to define content types such as “Course” or “Student” in a graphical way with the CCK module and visualize them with the Views module. However, this takes quite some initial work. Moreover, changes to the structure (e.g. allowing courses to have associated pictures of student projects) requires changing all this again. I believe that I should be able to change the structure of my homepage at any time. Adding a related publication to a software project or to a Master’s thesis should not involve a whole day of editing content types. Although I could use the Page content type for all my content, this is considered bad practice since Drupal only uses Page for static pages that almost never change. Of course, using Drupal only to provide a shared template and a global menu is massive overkill

In the same period, I read an interesting blog post on Academic Productivity about using a wiki to invisibly power a (research) homepage by Dario Tarborelli. A wiki seemed to provide a solution to structural flexibility, since it allows users to quickly rearrange content. However, as Dario points out, there are two problems that often make people suspicious of using a wiki for their website:

  1. anyone can edit the content of a wiki
  2. wikis look wikish

Dario demonstrates in the blog post that WikkaWiki can easily overcome both issues with access control lists and an easy-to-use skin system. He continues by giving a few advantages of using wikis for content management:

  • they allow you to edit and modify content at the speed of light
  • they allow you to easily embed all sort of contents in a page
  • they allow you to set granular access privileges for specific pages, which is a very powerful solution for collaborative work with colleagues and coauthors

I started to experiment with a WikkaWiki-based homepage and was able to very quickly migrate my content and create a custom skin. I was impressed! There was a catch though. WikkaWiki did not support file uploads in an easy way, and custom markup (e.g. lists with a certain CSS class) seemed to be hard to achieve. Having the ability to upload files was essential for me, since I did not want to use an (S)FTP client everytime I wanted to add a publication or screenshot. Custom markup would be nice to style my publications list. Although WikkaWiki supports embedding HTML directly, it is obviously not ideal to have large amounts of embedded HTML in the content of a page.

Then I decided to have a look at PmWiki . I already heard about PmWiki before. Jori used it to power his homepage, and Peter also used it to power the Mobile and Pervasive Computing course website. Of course, the fact that 6th most frequent author in HCI uses PmWiki to power his personal homepage and the homepage of his research group helps as well A few other examples of PmWiki usage by HCI researchers or groups:

But the question was of course: how can I use PmWiki to invisibly power my website? I decided to post a message on the PmWiki mailing list asking for help, and got many helpful responses. One of the things I especially like about PmWiki is the helpful and lively community. Everything I wanted to do with PmWiki was either explained in the Cookbook, or pointed out by someone on the mailing list. As an example of a very nice website invisibly powered by PmWiki, take a look at the Village School website.

These are the steps that I followed:

  1. Install PmWiki: this is very easy, just extract the archive and point a web browser to pmwiki.php (detailed instructions). PmWiki does not require a database, it uses flat files (yes, flat files!). That means you can easily copy a PmWiki installation from one directory to another (or even from one server to another).
  2. Create a new skin by copying the default pmwiki skin in a new directory and give it an appropriate name.
  3. Start editing the page template and CSS file to suit your liking. Hide typical wiki elements with CSS or by removing them from the template. PmWiki supports conditional markup so you can change the displayed page actions based on your login status. For more information, see this post on the mailing list and the documentation about page actions. You can also add conditional markup to hide the PmWiki documentation pages from the sidebar. If you refer to images in your CSS file, just keep in mind that the path is relative (e.g. refer to pmwiki/pub/skins/myskin/icons/trash.gif as background: url(icons/trash.gif);).
  4. Set a password for editing pages.
  5. Set up file uploads (disabled by default). Once uploads are enabled, PmWiki will automatically create the uploads/ directory when you upload a file. You might have to change the maximum upload size.
  6. Set up clean URLs like Main/Homepage instead of pmwiki.php?n=Main.Homepage (preferably with mod_rewrite). This is a lot easier than it sounds due to the excellent documentation.
  7. Done! Now you can start adding your content.

A few other random tips:

  • You delete a page by replacing its contents with the word “delete”.
  • Conditional markup is extremely useful to hide content that you don’t want to show yet. Just surround it with (:if false:) and (:ifend:) directives.
  • PmWiki’s markup is very flexible. You can easily add CSS classes to elements (see WikiStyles) and create advanced tables (see Table directives).
  • PmWiki supports wiki groups. This allows you to structure your pages in namespaces, so you can have for example both a Research.Activities and a Teaching.Activities page.

Finally, here is the result:

My new PmWiki-based homepage

All in all, I am very happy with it. I especially like the fact that I can add or change content quickly, wherever I am. All I need is a browser.