NRC Promoting Slope One

My old research group at NRC is promoting the Slope One algorithm for recommender systems:

The performance of Slope-One is remarkable; recommendations can be culled from collection of a million rated songs in a matter of seconds.

Note that the people who make this statement are only indirectly related with the authors of this algorithm (Anna and me) and they certainly could have chosen to work with other algorithms now that we have left NRC for quite some time (2 years). They base these statements on in-house, independent implementations they have designed.

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Why libxml2 takes forever to transform XHTML files

For my Online XML Course, I process lots and lots of XHTML content using XSLT. Up until now, I avoided the libxml2 XSLT processor (xstlproc) because it was unacceptably slow.

Today, I found out what is happening. It loads all of the XHTML DTD files from W3C each and every time it processes an XHTML file. To get around the problem, use the –novalid flag when invoking the xsltproc command line. You might get warnings about problematic entities, so I suggest you try a DOCTYPE declaration like the following:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"[ <!ENTITY laquo "«"> <!ENTITY raquo "»"> <!ENTITY oelig "œ"> <!ENTITY nbsp " "> ]>

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kd-tree applet

k-dimensional trees are a clever way to select all points in a rectangle using O(sqrt(n)+k) time where n is the total number of points and k is the number of points in the range. I usually don’t care for applets as a way to illustrate results (though I have two on my own web site doing just that!), but this kd-tree applet is a great trick. I post this here because I want to use it in a course if I ever have to teach this concept. The applet is in the public domain, but was written by Jacob Marner.

I resisted posting the applet here, because I know Java can crash some browsers or create other trouble. Sad. Java is an ok language and I really wish it would work in the browser.

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Sex.com sold for $14 million dollars

Slashdot reports that the sex.com domain name sold for $14 million. Recall that people spend billions every year buying software, which effectively costs nothing to copy.

The best route, these days, to become really rich is to find a way to create something that effectively costs nothing to produce, though it may cost a lot to design, and then, find a way to make sure you are the only one who can make an infinite number of copies for free. The problem is that we are collectively wising up to this get-rich-quick scheme.

I think that a more durable model, though a much less effective one, is to find a way to offer a service nobody else can match. Google comes to mind. It is a model based on constant hard work which appeals a lot more to the Catholic boy in me.

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Saving Bandwidth with CSSTidy

My CSS files get verbose over time. CSS is just not a great language or else, I’m not very good at it. Anyhow, I found out about CSSTidy which is a nifty tool to optimize your CSS files. There is also an online version. CSS optimization is a cool topic and it might get to be quite a challenge as selectors become more complex.

However, given the following test:

montant { color: red; font-weight: bold; background:white; font-style: normal; text-align: center; } nom { color: white; background:white; font-style: normal; text-align: left; } texte { color: black; text-align: center; font-style: normal; background:white; text-align: left; }

CSSTidy failed to rewrite it in the obvious way:

montant { color: red; font-weight: bold; text-align: center; } nom { color: white; text-align: left; } texte { color: black; text-align: left; } montant, nom, texte { background: white; font-style: normal; }