The reason is that for each module it is useful to know the output information of other modules. For example in clause boundary mapping is useful to know the syntactic functions of words or at least exact morphological interpretation. On the other side morphological and syntactic disambiguation modules need information about the clause boundaries. First as many intrasentential clause boundaries as possible are mapped in the morphologically analyzed input. Some examples of applying disambiguation constraints The input of morphological disambiguator is morphologically analyzed text.
Morphological analyzer gives to any word all possible morphological readings.
Not all alternatives are correct in given context. The task of morphological disambiguator is to discard illegitimate alternatives as more as possible. The Correct tag is added manually to the correct readings. They help to check the effect of the rules. Contextually illegitimate analyses are discarded by constraints.