You should check with the building dept with this. In MI and OH if you attach a structure to a dwelling ,the new part must have a code compliant footing that in some way is keyed to the dwelling footing. In toledo we built a pole structure that was attached to the house,but it had a residential footing that was pinned w/rebar to the house footing. The posts were set in sockets on the footer. Looking back,it was never a problem and never shifted,but in the end it would have cost about the same to stick frame it.I would think that posts set below frost would be ok if your slab had a 18" or so rat wall with rebar that is attached mechanically to the posts,but the zoneing people may have a different oppinion.
edit) I fabbed the sockets with about a 12" x 12" base plate and the sockets welded up useing 1/4 x 6 plate. This was para bolted to the footing. The sockets were 12" deep,not the flimsy ones you buy that are castings.