What's in a name - Part 2

How to give a resource a name, an URI? Let's look at this statement:

movie:Terminator dc:creator "James Cameron".

Happy with that? This is a valid RDF statement, and you understand what I wanted to say, and your RDF machine will be able to read and process it, too, so everything is fine.

Well, almost. movie:Terminator is a QName, and movie: is just a shorthand prefix, a namespace, that actually has to be defined as something. But as what? URIs are well-defined, so we shouldn't just define the namespace arbitrarily. The problem is, someone else could do the same, and suddenly, one URI could denote two different resources - this is called URI collision, and it is the next worst thing to immanentizing the Eschaton. That's why you should grab some URI space for yourself and there you go, you may define as many URIs there as you like (remember, the U in URI means Universal, that's why they make such a fuss about the URI space and ownership of it).

I am the webmaster of http://semantic.nodix.net, and the URI belongs to me and with it, all the URIs starting with it. Thus I decide, that movie: shall be http://semantic.nodix.net/movie/. Our example statement thus is the same as:

http://semantic.nodix.net/movie/Terminator http://purl.org/dc/elements/1.1/creator "James Cameron".

So this is actually what the computer sees. The short hand notation above is just for humans. But if you're like me, and you see the above Subject, you're already annoyed that it is not a link, that you can't click on it. So you copy it into your browser address bar, and go to http://semantic.nodix.net/movie/Terminator. Ups. A 404, the website is not found. You start thinking, oh man, stupid! Why you giving the resource such a name that looks so much like an web address, and then point it to 404-Nirvana?

Many think so. That's because they don't grasp the difference between URIs and URLs, and to be honest, this difference is maybe the worst idea the W3C ever had (that's a hard-to-achieve compliment, considering the introduction of XML/RDF-serialisation and XSD). We will return to this difference, but for now, let's see what usually happens.

Because http://semantic.nodix.net/movie/Terminator leads to nowhere, and I'm far too lazy to make a website for the Terminator just for this example, we will take another URI for the movie. Jumping to IMdb we quickly find the appropriate one, and then we can reformulate our statement:

http://www.imdb.com/title/tt0088247/ http://purl.org/dc/elements/1.1/creator "James Cameron".

Great! Our subject is a valid URI, clicking on http://www.imdb.com/title/tt0088247/ (or pasting it to a browser) will tell you more about the subject, and we have a valid RDF statement. Everything is fine again...

...until next time, where we will discuss the minor problems of our solution.