[UAI] How to estimate the parameters of a Noisy-or belief Network?

[ruan tong]

Hi,
        I use Noisy-or belief network in information filtering. But I  do
know how to estimate the paramter (Namely, Cij)from data. Futhmore, there
are hidden variables in the network, I do not know how to deal with them.
Maybe EM algorithm is workable.
        I wonder general methods of parameter estimation in belief network
can apply to Noisy-or model, or there are may-be good methods for
simplified networks. 
        Thanks in advance  for any suggestions. 

Tong.