We have seen that in the BookWarehousingBPEL process we already have six variables. All of them are MessageType. The inputVariable activity holds the message payload required for the process input. The outputVariable activity holds the response that the process will return. The BookstoreARequest activity holds the request message for the BookstoreA partner link, and the BookstoreAResponse activity holds the response message for the same partner link. The BookstoreBRequest and BookstoreBResponse activities hold the messages for the BookstoreB partner link, respectively.

We will first learn how to declare XML type variables. We will declare two new XML type variables in the BookWarehousingBPEL process. First, we will declare a BookstoreLocationWithLowestStockQuantity variable. This variable will be of the type string. We will use this variable to store the name of the bookstore that has the lowest stock quantity of the selected book.

Another simple type variable will be LowestQuantity, which will be of the type int. We will use this variable to store the lowest book quantity in any of the bookstores.