This project file contains model elements that are not part of a source model. When you build the project (on the Database ...

This project file contains model elements that are not part of a source model.
When you build the project (on the Database menu, click Project, and then
click Build), these model elements will be lost unless you migrate them to a
source model now.

Do you want to preserve these elements by migrating them to a new ER
Source Model?