upstart socket activation

[Steffen Barszus]

I have read about socket activation feature, and i'm quite
confused now and would like to have a definitive answer.

Is the socket activation:
a) xinetd like: start the provider of the socket, once the socket is
accessed ? Anything special done until the provider is available ?
b) can it also be used, that IF the provider is started, to start the
client of it at this event. (so basically reverse)

i would like sto start the client as soon as the server is providing
the socket for it (network or file)

Can you please explain ?