Dear all,
I have a problem understanding how subsumption and constraining
equations work together in the XLE. As far as I can see, XLE's behavior
is different from what the documentation says, but I am not sure I
understand.
The basic problem is this: I want to allow nominalizations of S's that
have a CASE value but not other S's. The rule I use is this:
NP --> { N' |
S: ! << ^
(! CASE)
}
So an NP can expand to S, in which case the S's f-structure should
subsume that of the NP, so all the information gets passed up from the
f-structure of the S to the f-structure of the NP. Then there is a
constraining/existential equation requiring the S's f-structure to have
CASE - or so I thought. It wouldn't be enough that the NP gets assigned
CASE from above, so to speak.
If I read it correctly, he documentation of explicit subsumption says
that it behaves differently from implicit subsumption (in sets) in that
constraining equations don't get distributed. But as it happens, XLE
accepts a solution where S in itself has no case, but the NP gets case
from the verb. So even though it displays two different f-structures for
the NP and the S (since they differ in CASE), it allows for the
existential constraint to be satisfied in the "wrong" f-structure.
I can achieve the effect I want by adding @(COMPLETE(! CASE)), forcing
local satisfaction of the existential constraint. In that case, there is
no need to use subsumption at all, of course. So implementation-wise I
am ok, but I am interested in subsumption from a theoretical point of
view as well, so if anyone can help explain XLE's behavior and whether
there is a particular theoretical reason for it, I'd be grateful. I have
a minimal implementation which recreates the problem, if anyone is
interested.
Best,
Dag Haug
