Hi,
So the effect here is that the externally defined CASE feature is propagated down the subsumption chain, as if it was an equality? But then, if there were also an equation (^ XXX) = ! on the S, we should see that the f-structure of the XXX has the case feature that Dag says we don't see when we look at the f-structure corresponding to the S. Is that what's happening?
In any event, I don't remember this particular twist or any motivation for it.
The closest I can come (which isn't too close, actually) is that this may have been tied up with an issue that Annie and I discussed in our paper on German partial VP fronting (LFG02), one of the papers that came out of our early subsumption work. The gloss of an exemplar sentence was
[The book to give]VP seemed Hans the girl.
meaning
Hans seemed to give the girl the book.
In our account we asserted that the f-structure of the topicalized VP is a subsumer of the f-structure complement of "seemed", which also includes the NP's that appeared in normal complement position. So we had the assertions (! TOPIC) = ! ! << (^ XCOMP* XCOMP) on the fronted VP. This reassembled everything as needed, but also kept as a separate unit the material that was topicalized, e.g. to account for discourse or other phenomena.
We noted that this created a problem for the original KB 82 definition of completeness. The fronted VP contains a PRED that is missing some of its arguments, and therefore would be marked as invalid according to the original definition of local completeness. We extended the definition so that an f-structure would be complete if it subsumed a complete f-structure, that is, completeness is tested only at the top of a chain of subsumptions.
So this has something to do with an interaction of subsumption with PRED-containing f-structures, and maybe that somehow impacted the implementation in this particular way. But it doesn't obviously relate to the problem at hand. The only point of the analogy is that the completeness existential constraint is evaluated on a structure that has assembled information from different levels of the subsumption chain.
I haven't found (and don't remember) any discussion of this situation. Maybe Annie does?
--Ron
On 5/16/12 10:17 AM, "Dag Haug" d.t.t.haug@ifikk.uio.no wrote:
Hi John,
thanks, that explains the XLE's behavior. I think you are right that explicit subsumption isn't used that much, but there has been some theoretical interest and for that reason it would be useful to be able to test it in various contexts without conversion to regular set subsumption. One day...
Dag
On Tue, 2012-05-15 at 15:25 -0700, John.Maxwell@parc.com wrote:
Hi Dag,
I looked at the XLE code, and there is special code that changes explicit subsumption to regular set subsumption if the f-structure has a predicate (which ! does). I don't remember adding this code, so I don't know what the linguistic justification is for it was.
Ron or Tracy would be better candidates for explaining the original justification for explicit subsumption in general.
Cheers,
John
On 5/15/12 1:36 PM, "Dag Haug" d.t.t.haug@ifikk.uio.no wrote:
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
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