There is no fixed defintion of DP. However, the US SC has attempted to define what a "Liberty" is, and the pursuit of happiness is mentioned.
One has a right to enage in the "common occupations of life", enter into contracts, marry, bring up a family, etc.
If you want to bottle the oxygen that surrounds you, as long as you do not misrepresent what it is, sure you can sell it, ever here of a pet rock?
If you are a chemist and wish to seperate the Nitrogen and bottle it and sell it, you need a license!!

