[wsrp][wsia][wsrp-wsia joint itnerfaces] Actions

I would like to open another discussion parallel to our session debate.
From the perspective of the protocol defined in the latest draft I can't
figure out the semantic difference between performAction and
getFragment.  Each seem to be capable of returning the same stuff.  Why
do we need both?  I.e. how are they semantically different?
     -Mike-