Equation 4illustrates that a good model will provide high probabilities to P (D|f )P (e|f, D) for bilingual sentence pairs (f, e).
for the same reason, a good domain definition will lead to a higher probability for the term: we define the domain D as that which maximizes P (D|f )P (e|D) (an approximation of P (D|f )P (e|f, D)).