This class links the Billable Service with the Billing Events in which the Health Plans are invoiced for the service There will typically be one or more Billing Events for a Billable Service: one if benefits are not coordinated among multiple payers (assuming no re-billing is needed); many if benefits coordination takes place (or if some kind of re-billing is needed for a single payer). This relationship is modeled as zero to many because a Billable Service may exist before a Billing Event is created for it, and it is possible that no Billing Event might occur in the case of cash payments or if the fee is written off.