[developers] Dropped arguments in DMRS

[Stephan Oepen]

hi again,

> For Mike's examples, where the dropped arguments are necessarily coindexed,
> the case for representing this in the DMRS is more compelling.  So my
> thoughts are that the DMRS simply includes a node with a standard predicate
> (e.g., `unexp', but any name you all want as long as it doesn't clash with
> something already in use) which is a grammar pred and is linked to in the
> usual way.  So more-or-less equivalent to the zero pronoun analysis,
> assuming the zero pronouns don't have quantifiers.  Is this done with EDS?
> I'll match terminology etc if so.

i believe EDS and DMRS currently behave alike in this respect: there
is one node per EP, such that unexpressed arguments in the MRS
disappear in the dependency graph, even if they were co-indexed across
EPs.

if we were to add code to synthesize nodes for variables that are not
introduced as the distinguished (or characteristic) variable of any EP
but occur at least twice in an MRS, it would seem natural to me to
leave these nodes unlabeled (they will not have characterization or
other surface links either).  this would also indicate that they have
a somewhat different status formally (at least in terms of
correspondences to a full MRS).

i share your sentiment that the disappearing of unexpressed arguments
in our dependency graphs in general reduces clutter and is desirable.
co-indexation of such (unexpressed) variables admittedly challenges
that position.  if we end up special-coding for these cases, it would
be good to have the motivating examples and analyses readily available
(and publicly vetted).  i believe emily may have been the first to
argue for such co-indexation, probably from her work in the
grammarium?

—i recall we have talked once or twice in the past about adding an
explicit distinction of unexpressed variables.  for the ERG at least,
i believe dan (and others) often look at ‘u’ and ‘i’ (and maybe ‘p’)
as varible sorts that indicate unexpressed arguments.  but that is at
best a convention and prevents stronger typing of argument slots as
would be desirable.  for example, the ARG2 of _eat_v_1 presumably must
always be an ‘x’ when expressed, but dan abstains from putting that
type into the lexical entry because the scoping machinery would
complain at ‘x’-typed variable without a quantifier.

would it work (and be desirable) to introduce a variable property, say
[ XP bool ], to distinguish expressed from unexpressed roles?  i
imagine it would not be hard to make all constructions that bind roles
specialize XP to true; one could then use the VPM machinery upon MRS
read-out to default remaining (unspecific) XP values to false.
alternatively, i imagine one could obtain the same effect by making
the hierarchy of variable types a little richer, i.e. put something
above at least ‘x’ and ‘e’ to indicate unxpressed variants, say ‘w’
and ‘d’ (the immediately preceding letters :-).

any thoughts on actually introducing such an explicit marking of
unexpressed arguments?

all best, oe