Sparx EA does not really support IDEF0, because..
*In Sparx, a line MUST connect two boxes*, whereas IDEF0 ICOMs have only one connected end, except for transitions (which are at once an output and input).
ICOM arrows are objects, but Sparx uses boxes (i.e. classes) for objects.
I have created a form of IDEF0 using MDG, but it's tortured.
The beauty of IDEF0 is that you can use a very simple set of shapes to convey a ton of information in a very small space. You really cannot do that if you have to create a box for ever object.
Don't really see a way of doing this in Sparx without a major deviation from the core program model.