sorting elements

Hi people,

I have to sort some elements that have the following content:

<art>1.1</art>
<art>1</art>
<art>2</art>
<art>2.1.1</art>
<art>2.1</art>

and the order should be 1 - 1.1 - 2 - 2.1 - 2.1.1

What method should I use? because the value that I've to use for sorting has a hierarchical meaning..
Any idea?

Thanks!!

Esteban