App Studio creates a JSON Data Transform when you Add (or Replace) the Data Source for a Data Object, and you specify a JSON-over-REST API. The JSON Data Transform defines the mapping rules for transforming between an instance of the Data Object and its corresponding JSON message. Irrelevant parts of the JSON message can be ignored. In these circumstances, there is no longer a need for an elaborate Class Model in the integration layer to mirror the schema of JSON messages - this is encapsulated within the JSON Data Transform(s).
Dev Studio still has the REST Connector wizard from Pega 7 which creates *-Int-* Classes and Properties that mirror the components of JSON messages in the Request and Response. This approach is, however, less performant than the JSON Data Transform approach adopted by App Studio.
The wizards from each Studio allow any existing JSON files that represent the Request and Response messages for a JSON interface to be used by the wizard in the event that a live API is not available.