Sort of both.... you can put it in the ground, then chop it at some point. Then choose one of the new buds that you will get to be a new 'leader', let that grow out for a while, and chop it again higher. That way, you get a tapering trunk that diminishes diameter as it goes upward.
Depending on how fast or slow growing the oak is, a chop may only be needed once every year or two.
Pick up one of the Peter Adams books, he gives great advice about understanding trunk chops. Also go on Evergreen's website and read his articles...
www.evergreengardenworks.com
Joanie