al subject in a passive expression
without "by" phrase), it is shown as "UNKNOWN".

<p>
The position of a word is represented with an integer starting from
zero.  In the example, the position of "Enju" is 0, "is" is 1, ... and
"parser" is 6.  Words whose POS is "." (e.g. "." and "?") are
ignored.  The position numbers of "ROOT" and "UNKNOWN" are output as
"-1".

<p>
The label of a relation is represented with one of "MOD", "ARG1", ...,
and "ARG4".  "ARG1" is for a subject of a verb, a target of
modification