Let’s consider the example where we ask the email service to send an email when an order has been shipped. Now we could send in the request to the email service with the customer’s email address, name, and order details. However, if the email service is actually queuing up these requests, or pulling them from a queue, things could change in the meantime. It might make more sense to just send a URI for the Customer and Order resources, and let the email server go look them up when it is time to send the email.
Entity by reference
