Hi Peter
To automate this you would need an audience rule that selects the people who have completed the seminar activity. Audience rules don't go down to the activity level - they do go to the course level.
If the seminar completion completes the course then a rule for course completion could be used to select these people to enrol in another course that has the content for this audience.
Programs also allow for setting a learning path so one course is required to be completed before another course is able to be enrolled in.
regards