[storm] question about valitation

[Massimo]

Hi everybody,
I have another newbie question, please beg my pardon...

I'm wondering how to implement a "validation" function for a storm 
class/object.

For instance, let's suppose i have to implement an object that is 
correct only if field x is greather than field y. I would write a 
funciont (e.g. validate(self)) that returns some "false" value if x<=y, 
to prevent insert/updating non valid objects.
Where and how soul I write such a function in the Storm system?

Thanks in advance,
max.