Data Model Design Q: Translation

FROM : Ben Lachman
DATE : Tue Jul 11 22:38:10 2006

I'm wondering how to design my data model so that I can include a 
substitution/translation object in my model.  Basically I want an 
object that says 3 of this thing is equal to 4 of that thing, where 
the things are of the same class.  A basic example would be 
substituting change:  5 pennies are equal to 1 nickel, 4 nickels are 
equal to 2 dimes, etc.  The inverse of these is always true as well. 
This makes sense and seems pretty simple, but I can't figure out a 
decent way of doing this within the xcode data modeler.  What I'd 
like is something like this:

[ Coin ] <---->> [ Substitution ] <<----> [ Coin ]

where [ Coin ] has a substitutions to-many relationship and 
[ Substitution ] has a pair of amounts (5 and 1 for instance) and 
relationships (to the nickel and penny coin objects).

Does anyone have an idea of how to do this in xcode?

Thanks,

->Ben
--
The user's going to pick dancing pigs over security every time. — 
Bruce Schneier