MaltParser has the possibility of distinguishing between different kinds of null-values when extracting the feature
vector. For input columns like
POSTAG it is possible to differentiate two null-values:
NO NODE: There exists no corresponding dependency graph node (e.g., because the lookahead extend beyond the end of the string), which means that the feature is really undefined.
ROOT NODE: The dependency graph node is a root node, which means that it is not possible to extract an input column value (for example, the word form or the part-of-speech).
In addition to the two null value categories for input columns, there is one more for the output columns:
NO VALUE: The dependency graph node exists and is not the root, but has not yet been assigned a value for the output column requested (e.g., has not been assigned a head and therefore does not have a dependency type).
--singlemalt-null_valueit is possible to specify the degree of differentiation of null-values.
none: Excludes all kinds of null-values when extracting the feature vector, this option value is not possible for learning methods that have symbolic feature vector encoding.
one: Maps all kinds of null values to one symbol.
rootlabel: Maps all kinds of null values to one symbol and for output columns this symbol is the same as the root label (used to emulate MaltParser 0.4)
rootnode: Distinguishes between
ROOT NODE, and the
NO VALUEnull-value case is mapped to the
ROOT NODEnull-value for output columns.
novalue: Distinguishes between
ROOT NODEfor both input and output columns, and
NO VALUEfor output columns.
Copyright 2007-2017 Johan Hall, Jens Nilsson and Joakim Nivre.