3.4.1 Abstract Data Model
This section describes a conceptual model of possible data organization that an implementation maintains to participate in this protocol. The described organization is provided to facilitate the explanation of how the protocol behaves. This specification does not mandate that implementations adhere to this model as long as their external behavior is consistent with that described in this specification.
The client MAY use a Boolean flag, PiggybackNotifyEnabled, for each subscription to track whether piggyback NOTIFY is supported for that subscription.
The server MAY also use a similar Boolean flag, PiggybackNotifyEnabled, for each subscription to track whether piggyback NOTIFY is supported for that subscription.
Note that the preceding conceptual data can be implemented by using a variety of techniques. An implementation is at liberty to implement such data in any way convenient.