In some cases, it could be useful to either add a new feature-value to the head or modify the value of one of its features. These two operations can be performed by making use of operator “Add”. For instance, the list of morpho-syntactic features used by DepPattern does not contain the verb property “voice”. The operator allows to introduce a new feature specifying the voice of the head verb (passive or active) after having applied a grammatical rule. For instance, consider a pattern identifying a semi-auxiliary verb (dependent) occurring to the left of a past partiple verb, its head (as in the expression “was eaten”). Operator “Add” can be used to assign the passive voice to the head verb:
SpecifierLeft: VERB<type:S> VERB<mode:P>
Add: voice:passive
%
This new morpho-syntactic information, introduced by a grammatical rule, can be used as the input in further rule applications.
Notice that Add can be very useful to correct systematic errors made by the tagger, since it also allows modifying values of existing features.
