Joomla! only recently formed a working group for "Web Services" and I think you won't see any outcomes from that for a while.
As @Riccardo Zom, say your best bet will be to access the barest formats you can from each component type using the format
/tmpl
parameters.
If you're motivated enough you could extend existing components (core and otherwise) to return the desired format (e.g. json
), in that case you should read Louis Landry's note on the changes from 1.5 era XML-RPC
feature set to the 1.6/2.5 mechanism.
If you're still looking after that you may be interested in the "Joomla! API - Generic RESTful API framework for Joomla! 2.5" by Rafael Corral, it's a component (com_api
) that provides a framework for creating a RESTful API for a Joomla! 2.5 site.