When a record contains type 1 data, there is only one level of fields under the subject that identifies the record.
Here's a record containing type 1 data. It's a quotation in a foreign exchange trading system, and the subject is
When a client first subscribes to
/EURUSD, it receives a type 1 record containing all the fields with their latest values (assuming the client didn't exclude any of the fields from the subscription). Subsequently whenever the client receives an update to
/EURUSD, the record contains just the fields whose values have changed.
Whenever an update arrives in a DataSource application for any of these fields, the value is overwritten. A client newly subscribing to
/EURUSD would then see this new value; the previous value would not be available.