After selecting a Start table to create a new Source Definition all child tables are missing on the RC/EXTRACT Source Definition panel. Using command MODESW result in message 'RX190I: There are no relationships to display'.
Check the RC/Extract Profile and make sure option 'Select Entire R/I Set' is set to Y
You can update the profile from RC/EXTRACT Main Menu or by command PROFILE.
Then create a new Source Definition.
You should now see all child tables listed.