Account Telephony Sessions Event - body["parties"] Primary Key

We have subscriptions set up to get the party information from the Account Telephony Sessions Event Notifications (https://developers.ringcentral.com/api-reference/Account-Telephony-Sessions-Event). I see that the body["parties"] is a list which means we could see more than one party for a given UUID. If that is the case then what fields would make the body["parties"] unique? In database terms, what is the Primary key of the body["parties"]?