Please see my comment to the question: it depends on a number of factors. Just one thing you might want to look for is LINQ to XML
However, this is only one of possible approaches. The only reason I mentioned it is universal, so it does not depend much on the detail missing from the question. When you consider all relevant detail, some other solution may appear much better. As I don't even know your motivation for using "XML database" (whatever it is), I'm not sure that even this is the right decision for you. It has the minimum overhead (no third party codes), but majorly depends on volume of data and scalability you need. With certain scalability requirements, I'm not sure that you could through out the idea of using some relational database instead.