5.2 Relationship between requests and notifications

The MessageId sits at the message level and uniquely identifies an entire message instance. Within that message, the ClusterId identifies each individual cluster to be communicated. Each cluster contained in a message must be uniquely identified by the MessageSender; this identifier is used to refer to that cluster in all subsequent messages.

Parties that create a cluster shall therefore ensure that any ClusterIds, shall be, in combination with the DdexPartyId (DPID) of the cluster creator, globally unique.

Depending on the circumstances, the same identifier may subsequently appear as a RequestedClusterId or a ClusterCreatorClusterId in a response message.

A MusicalWorkClusterNotification may be in response to none, one or more MusicalWorkClusterRequests or MusicalWorkClusterNotifications.

When a MusicalWorkClusterNotification is intended as a response to a MusicalWorkClusterRequest, the sender shall include the ClusterId originally assigned by the sender of a request message into the RequestedClusterId tag. It is only required when the MusicalWorkClusterNotification message explicitly responds to a request message, enabling the recipient to correlate the response with a specific, previously requested cluster.

When a MusicalWorkClusterNotification is intended as a response to another MusicalWorkClusterNotification, the sender shall include that ClusterId originally assigned by the creator of the cluster in the ClusterCreatorClusterId to maintain a robust linkage between the clusters in related MusicalWorkClusterNotification messages.