Is it mendatory to create the items in MIO or any inventory Org?

Dear Experts,

Is it mendatory to create the Items first in MIO or any inventory Organization and then assign the purchasing category and after that swith to the iprocurement and Map the purchasing category with the shoping category defined in the iprocurement?

As i seen in the solutionbeacon instance that the items are showing in the iprocurement but they are not setup in any inventory Organization or I might be wrong, so want to just conform?

Reagrds,
Jahanzeb