I'll use a metaphor:
During the creation of a supervisor object, the user can select one or more existing employees (peers) to assign to the supervisor. As a rule on the Supervisor, I want to determine whether any employees have been assigned and if so, send an email notification to each. I can't figure it out any syntax that works.
Not workable but expresses the idea:
IF EXISTS Employee IN Supervisor.Employees THEN
Since the object may not be committed to the database at this point, I am unsure if this is feasible. It's probably really easy like all things in AIM and I'm just over thinking it.