Hello, I have not been able to find a way to create a relationship between two tables in the same model, but in different workplaces.
Do you mean to create a shortcut of a relationship that already exists in another workspace?
If so, simply select the relationship in WS where it exists, right-click and select Add into Workspace. Select the WS where you like to add this relationship.
Another way: open Designer of the WS where you like to add the relationship. Rright-click the WS, select ‘Complete from Model’ and select the relationship.
I recommend to see the Help file | Index tab where you write Shortcuts - click the topic Using Shortcuts for more details.
Practical examples can be found in Manual | Index tab where you write Shortcuts as well - click the topic Using Shortcuts.
If you have any questions, please write me back.