In Visio, one can define custom data fields on an object.
Let's say that I have two objects: Object_A and Object_B. Object_A has a user-defined variable: Var1.
If Object_A.Var1 = 0 then don't show Object_B. Otherwise, show it.
The actual showing/hiding can be accomplished via the object's transparency setting, but I don't know how to have one reference the other outside of writing a macro.