Using XML with Legacy Business Applications

Is There Data or Not?

It is customary to specify that certain data must be present in a document before it can successfully be imported into a business application. Many people coming from an EDI background are very accustomed to having their EDI systems verify that essential information like purchase order numbers and item IDs are present in a message. They look to schemas and schema validating parsers to help them enforce these types of constraints. However, things in this area don't quite work as many people expect. I can best show this with an example.

Let's consider a simple invoice. Our customer requires us to send them back their original purchase order number when we send them an invoice electronically. They have set their PurchaseOrderElement ...