Conceptual model with a constraint

Question

I'm trying to make a conceptual model of this use case:

The Actor can modify the budget but after the modification the sum of all the budget elements percentages must be 100% or 0% if there are no elements in the budget.

How can I include this constraint in my model?
The model can also be found here

Answer 1

You should just put a constraint on the contains property. In MagicDraw one can show the label for a constraint or the actual constraint in OCL.

Here is an example with the label only, which is probably more appropriate for the audience of a conceptual model:

Here is an example with OCL:

A little less readable, eh?

Answer 2

Simply attach the constraint like this to Budget

You can simply use a Note and put the constraint in curly brackets if your tool does not provide a native constraint element.