XML makes communication easy. It's a great tool for transactions between businesses. XML is used to aid the exchange of data by making it possible to define data in a clear way. Both the sending and the receiving party will use XML to understand the kind of data that's been exchanged—by using XML, everybody knows that the same interpretation of the data is used. For several years, Electronic Data Interchange (EDI) has been the way to exchange data between businesses. EDI is expensive because it uses a dedicated communication infrastructure, and the definitions used are far from flexible. XML is a good replacement for EDI because it uses the Internet for the data exchange and it's very flexible. Also, a growing number of programs, such as Microsoft Office, now store data in XML format and can easily export this data, allowing it to be used and reused on websites.
In addition to the exchange of data, we can define other languages with XML. A good example is Wireless Markup Language (WML), the language used in WAP (Wireless Application Protocol)—communications on mobile phones. WML is just an XML application.