UML/XMI and semantic web

Hi!

I'm evaluating XML-based technologies for a tool providing interoperability 
on the data level between different systems in the tourism domain. 
Naturally the question of building ontologies has came up. Observing the 
research in this area it is still unclear to me whether it is 
possible/feasible to use UML as modelling language for onthologies and then 
XMI in order to provide a machine readable form? Please give me some pros - 
contras, considering UML/XMI and let's say OIL based modelling. I'd also 
welcome some related URLs.

Thanks!

oliver