Two of XML's biggest strengths are its abilities to represent arbitrary types of data (e.g., purchase orders, financial transactions, calendar items) and to provide a platform-neutral format for exchanging data between business partners. Once you've decided to exchange XML data with your business partner, you need to agree on the XML grammar you'll use to exchange the data. You'll either invent your own custom XML grammar or adopt a predefined, industry-standard grammar such as the XML Common Bu...