Take a look to this links: msdn.microsoft.com/.../hh173661%28v=nav.70%29.aspx
Hope this helps!!
You are saying is correct.
In order planning you can plan based on actual demands that are Production demand, Sales demand, Service demand, Job demand & Assembly demand. As the name of the page says "Order planning" is does not include production forecast.
Whereas you have an option to include production plan if you want to include it in material planning.
One more difference between order planning and planning w/s is that order planning suggests planning for one level (low level code) only, of more then one low levels are involved then you will need to re run the order planning and plan for next low level code. Whereas planning w/s considers all low levels associated to create an item.
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