Problems with Multi-tier applications and XML DOM

Hi people, I have a question about developing Multi-tier applications and XML. I`m currently developing such a application, but i am stuck. I ve a database abstraction layer and a data acces component (in the data layer), and in the logic layer a class that builds (or should build) XML. The presentation layer consist of multiple XSL stylesheets and some classes to convert XML to HTML or whatever other type of content. My classes in the datalayer currently either returning an object or an (two) dimensional array, wich should then be converted to XML in the logic layer. This is where i get stuck though.. My database abstraction layer is also capable of outputing an XML document, but this wouldnt be 3 tier.. How would you (the experts) solve this, what kinda aproach would you take. If you want i can e-mail some of the code, but its so much i didnt want to send it over this mailinglist... Thanks for the help already, i hope someone can help me. If someone has a good example that would be highly appreciated. ;-) Best regards, Davy Obdam