I can use a Report Definition to populate a Page-structure Data Page now? The Response Data Transform must be important!
Indeed it is. Response Data Transforms have been required when the class of data from the Data Source differs from the class of data of the Data Page that is presented to the application. This is the next logical step. The Response Data Transform can just as easily map list data (returned on .pxResults from a Report Definition) to the data model of a Page-structure Data Page.
Consider an application need to locate a Customer by their email address (assuming Customer data is stored in Pega), even though the key for Customer data is some other sort of Customer identifier. As the email address is not the key for Customer data, the Lookup Data Source cannot be used. As the data is held within Pega, a Report Definition can be used on the Customer data, filtering by email address.
If you were 100% sure that no more than one Customer record would have the matching email address, your Response Data Transform could map DataSource.pxResults(1) to Primary. This both:
Needs to be governed by a check that there is more than 0 results; and
Likely needs to determine which result to use if there is more than 1 result
This is entirely up to the Response Data Transform, but is now feasible in Data Page configuration without requiring an Activity to solve for this scenario.