What XML won't do for you

XML is a foundation, not a complete solution

Data is data While data files can do lots of things (even code is data at some point), data files need program infrastructure to be useful in computing processes.
Labelled structures only a start XML does a better (more accessible, easily processed, customizable)job of representing data than many competing formats, but creating documents doesn't create an environment which can process or even display them.
Agreements are limited and temporary XML purveyors promising the creation of one true format for XYZ vertical industry needs are delusional. While interchange formats are useful, they don't solve all problems of data representation. Between the need to evolve and the need to specialize, there will be some Babel.
XML tools only go so far There are all kinds of XML tools available for parsing, processing, transforming, generating, and storing XML. Now you just need to apply them to your XML.