[developers] Questions about the MRS algebra from Seattle

[Ann Copestake]

here's some quick answers (on the basis I may never get round to 
replying if I try and reply more carefully)

On 26/06/2015 22:13, Emily M. Bender wrote:
> Dear all,
>
> The UW group has been reading and discussing Copestake et al 2001
> and Copestake 2007, trying to get a better understanding of the MRS
> algebra.  We have a few questions---I think some of these issues have been
> proposed for the Summit, but I'm impatient, so I thought I'd try to get
> a discussion going over email.  UW folks: Please feel free to chime in
> with other questions I haven't remembered just now.
>
> The two big ones are:
>
> (1) Copestake et al 2001 don't explicitly state what the purpose of the
> algebra is.  My understanding is that it provides a guarantee that the 
> MRSs
> produced by a grammar are well-formed, so long as the grammar is
> algebra-compliant.   Well-formed MRS (in this sense) would necessarily
> have an interpretation because the algebra shows how to compose the
> interpretation for each sement.  Is this on track?  Are there other 
> reasons
> to want an algebra?

We have never managed to prove that MRSs constructed according to the 
algebra will be scopable, but I think that is the case.  But more 
generally, the algebra gives some more constraints to the idea of 
compositionality which isn't the case if you simply use feature 
structures.  It excludes some possible ways of doing semantic 
composition and therefore constitutes a testable hypothesis about the 
nature of the syntax-semantics interface.  It also allows one to do the 
same semantic composition with grammars in formalisms other than typed 
feature structures.

>
> Subquestions:
>
>  (1a) I was a bit surprised to see the positing of labels in the 
> model.  What
> would a label correspond to in the world?  Is this akin to reification 
> of propositions?
> Are we really talking about all the labels here, or just those that 
> survive once
> an MRS is fully scoped?

the model here is not a model of the world - it's a model of semantic 
structures (fully scoped MRSs).

>  (1b) How does this discussion relate to what Ann was talking about at 
> IWCS
> regarding the logical fragment of the ERG and the rest of the ERG?  
> That is,
> if all of the ERG were algebra-compliant, does that mean that all of 
> the ERSs
> it can produce are compositional in their interpretation? Or does that 
> require
> a model that can "keep up"?

it's really orthogonal - what I was talking about at IWCS was about the 
complete MRSs.

> (2) Copestake et al state: "Since the constraints [= constraints on 
> grammar rules
> that make them algebra-compliant] need not be checked at runtime, it 
> seems
> better to regard them as metalevel conditions on the description of 
> the grammar,
> which can anyway easily be checked by code which converts the TFS into 
> the
> algebraic representation."  What is the current thinking on this?  Is 
> it in fact
> possible convert TFS (here I assume that means lexical entries & 
> rules?) to
> algebraic representation?  Has this been done?
>

`easily' might be an exaggeration, but the code is in the LKB, though it 
has to be parameterised for the grammar and may not work with the 
current ERG. You can access it via the menu on the trees, if I remember 
correctly.  The small mrscomp grammar is algebra compliant, the ERG 
wasn't entirely when I tested it.

> Thanks,
> Emily
>
>
> -- 
> Emily M. Bender
> Professor, Department of Linguistics
> Check out CLMS on facebook! http://www.facebook.com/uwclma

All best,

Ann