A model of co-occurrence in bitext is a boolean predicate that indicates
whether a given pair of word tokens co-occur in corresponding regions of the
bitext space. Co-occurrence is a precondition for the possibility that two
tokens might be mutual translations. Models of co-occurrence are the glue that
binds methods for mapping bitext correspondence with methods for estimating
translation models into an integrated system for exploiting parallel texts.
Different models of co-occurrence are possible, depending on the kind of bitext
map that is available, the language-specific information that is available, and
the assumptions made about the nature of translational equivalence. Although
most statistical translation models are based on models of co-occurrence,
modeling co-occurrence correctly is more difficult than it may at first appear