Reentrancy in feature structures

[kay at cogsci.berkeley.edu]

On Wed, 3 Jul 2002, Mike Maxwell wrote:

> John Beavers wrote:
> > On Tue, 2 Jul 2002, Luis Casillas wrote:
> >
> >> 4. A tree satisfies an atomic path equivalence PATH1 = PATH2 iff the
> >>    the subtree rooted at the node reached by following PATH1, and the
> >>    subtree rooted at the node reached by following PATH2, are
> >> identical.
> >>
> >> As far as I can see, reentrancy is just a way of guaranteeing that 4
> >> will hold.  Am I missing something?
> >
> > Well, it seems to me that you've just replaced co-identification with
> > some notion of equivalence, and I don't think this makes a
> > difference.  It certainly wouldn't make any difference in whatever
> > way you build such models (even the problem of infinite recursion is
> > still an issue if a path is constrained to be equivalent to a
> > superpath).  As far as the models themselves, well, any dag you get
> > as a model can be converted into a tree algorithmically but you lose
> > the equivalence information as part of the data struture.  It seems
> > to me that's the only difference, and depending on whether you find
> > that kind of information useful it could be an unimportant difference.
>
> As a lurker on this list, let me ask a couple naive questions.  First,
> it seems to me that the meaning of "identical" in Luis Casillas'
> definition is a crucial issue here.  Dredging something out of my old
> lisping days, I recall that Lisp made a distinction between (at least)
> two notions of "identical", often labeled "eq" and "equal".  One (I
> can't recall which) required identity of content (so e.g. two strings
> were equal under this definition if they were "spelled" the same), while
> the other required identity of reference (i.e. they were the same memory
> location).  I presume that condition 4 requires the latter (stronger)
> definition, correct?  In which case the equivalency really is just the
> same as re-entrancy, correct?
>
> Second (and assuming the answer to the first question is "yes"), I can
> think of one obvious case where this sort of thing makes a difference,
> namely with co-reference.  E.g. in some language where verbs are marked
> for agreement with subject and object, you would get a reflexive form
> only where the subject and object agreement features were identical in
> the strong sense.  (Otherwise you couldn't distinguish the translation
> equivalent of "He saw him" from "He saw himself.")
>
> Are there other cases where the strong notion of identity is required,
> besides (person) co-reference?

Possibly there are ambiguities (or vaguenesses) in headless relatives that
might be captured with a distinciton like this.  Compare the ordinary
readings of

	I saw what he saw.
	I ate what he ate.

The two obvious readings of

	I wore what he wore.

involving either one outfit on two occasions or two similar outfits on one
occasion illustrate the contrast as an (apparent) ambiguity.

Paul


>      Mike Maxwell
>      Linguistic Data Consortium
>      maxwell at ldc.upenn.edu
>
>


__________________________________________________________
 Paul Kay                      Department of Linguistics
 kay at cogsci.berkeley.edu       University of California
 www.icsi.berkeley.edu/~kay    Berkeley, CA 94720, USA