Eric B wrote:

> -Is it OK to keep and work with 2 different types of variables inside a
> single GPData class?

Absolutely.  The GPData class can be customized any way you like.

> -Do I understand it well that I can use the ValueData.bool as a test and I
> can use ValueData.value as the result?

You certainly can.  It sounds like you have a handle on the general way 
that nodes can pass data to one another.  But you need to keep in mind 
that you may need to add explicit typing (see GPType) to make certain 
that various nodes connect together in the tree in such a way that if 
one writes to ValueData.bool to hand to his parent, the parent's not 
expecting a ValueData.value.