[rmrs] Questions on DMRS

[Michael Wayne Goodman]

Hi RMRS-list,

I'm working on adding DMRS reading/writing support to my Python MRS
library. I've read through the Slacker Semantics paper and comments in
the Lisp code, but I have some remaining questions. Sorry this email
turned out quite long; even partial responses would be appreciated.

* What does the paper mean by "head", as in Sec. 4.2 "Head selection
in the qeq graph". Is this like the heads of other dependency grammar
formalisms? It seems to, at least, be different from syntactic heads.

* According to the lisp code, if an LTOP labels of a set of EPs, then
"the LTOP node in the DMRS is linked to each head predicate in that
set". This "LTOP node" is implicit, yes? I see its ID is 0, but I
don't see the node itself being output anywhere.

* Regarding the LTOP link, should it be an undirected /EQ link? When I
try with the LKB, I see a link with no pre- nor post-slash content (or
rather, NIL):

<link from='0' to='10004'><rargname>NIL</rargname><post>NIL</post></link>

* Furthermore, why is there textual content "NIL" rather than an empty
element <rargname/>? Would an empty element be interpreted the same?
As it is, this seems like it would break if, ${deity}-forbid, some
grammar developer defined a "NIL" role for EPs, such that "NIL" is
actually the rargname. E.g.:
[ "_example_n_1_rel" LBL: h3 ARG0:x4 NIL:h5 ]

* Also related to LTOP links, when might we see the LTOP being linked
to more than one node? Admittedly I'm not very good at coming up with
examples, but I can't imagine such a sentence. Of course there's
things like "the dog barked loudly", where "loudly" and "barked" share
the label identified with LTOP, but in this case there would only be
one link going to the head of the label-equality-set: "loudly".

* I'm also interested in DMRS-MRS conversion, and so I'd like to
recover the INDEX. I currently look for EPs that have no arguments
within their label-eq-set, and are not the argument of an EP outside
their label-eq-set. This by itself mostly works, except it can't
select between "bark" and "maybe" in "some dogs bark maybe". I can
exclude "maybe" if I look for EPs that don't have a hole argument
QEQing some other EP's label, but then I fail to select "and" in "some
dogs bark and sleep" (since L-HNDL and R-HNDL are hole arguments on
"and"). I could then refine this so it ignores EPs QEQing some other
EP only if the other EP's ARG0 isn't also an argument of the original
EP (e.g. "bark"'s label is QEQed from "and"'s L-HNDL, but its ARG0 is
also "and"'s L-INDEX), but now it feels like a hack. Is there a more
reliable way to do this, preferably without loading the grammar and/or
the SEM-I?

Thank you,

-- 
-Michael Wayne Goodman