The purpose of the Update Purchaseorder is to request another business application to make Updates to an existing Purchase Order. This Update must refer to the original document and/or item ordered. The Update processing assumes replacement of fields sent, with the exception the identifying fields of the Purchase Order. If any of these key fields require changing, (i.e. the PurchaseOrder Document Id or a LineNumber) that constitutes a cancellation of the request and/or the addition of another Purchase Order. Is where the information that the BOD message carries is provided, in this case UpdatePurchaseOrder. The information consists of a Verb and one or more Nouns. The verb (Update) indicates the action to be performed on the Noun (PurchaseOrder).