I'm in a situation that is the following:
Company is an aggregate root and contains a list of contacts (name, phone, ..).
On another aggregate root "Contract" you are able to add something called "Participants". A participant could be a company or a contact from a company.
As far as I know, DDD doesn't allow to hold a reference in this "participation" to the ID of the contact below the company AR.
How is this solved?