ATP and non-ATP inventory system

A brief answer here is as follows

(1) to be able to add an item to an cart - OderItemAdd
(2) to be able to update an item in a cart - OrderItemUpdate
(3) to delete an item in a cart - OrderItemDelete
(4) to associate a shipping address to an order - OrderItemUpdate
(5) to associate a billing address to an order - OrderItemUpdate
(6) to lock an order in commerce - OrderPrepare
(7) to submit an order for processing - OrderProcess 

ATP and non-ATP inventory system supported by WebSphere Commerce

There are several differences between the ATP inventory system and non-ATP inventory system.

ATP store	Non-ATP store
It supports stock allocation from an existing or expected inventory and it also supports future order.	It only checks, allocates or reverses base on existing inventory.
It tracks the inventory on hand, in process, in reservation, on backorder, expected,	It only tracks inventory on hand.
It can specify shipment as complete for all order items in one order, and can also support expedited. It supports track inventory on the kit level. Dynamic and static kits' inventory information is tracked at the kits' component level.	It does not support track inventory information for dynamic kits or static kits at the component level.
It can split order item due to insufficient inventory on one fulfillment center.	It cannot split order item.
It supports capturing of information such as requested ship date, ship as complete, expedited orderitem and ship tie code. It supports order processing with this information.	It supports capturing of information such as requested ship date, ship as complete, expedited orderitem and ship tie code but does not support order processing with this information.