As u may know B2B is Business-to-Business. This literally means communication and exchange of valuable data between business. Now, where does XML come in? XML as it's name suggests, is "Extensible". What this means is that You and I can agree upon a format (tags) to communicate with each other. We can thus share data in a format that is understood by both of us. However, we may be using entirely different databases, servers, back ends or whatever.
Furthermore, if later, a third person wants to share data with us, and have access to our data (only if we allow it, of course
), then all he has to do is conform to our format (tags).
XML will NOT replace databases. It will only supplement them be giving them powerful capabilities. You may be using Oracle and I may be using DB2....but if both these databases support (and they do)..we can exchange data without any interface problems using XML.
Hope this helped clarify something.