[developers] Questions about the MRS algebra from Seattle

[Emily M. Bender]

Dear Ann,

Thanks for the quick answers!  Some further comments/questions below:

On Fri, Jun 26, 2015 at 4:09 PM, Ann Copestake <aac10 at cl.cam.ac.uk> wrote:

> 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.
>
>
I'm still trying to understand why it's important (or maybe interesting is
the goal, rather than important?) to exclude some possible ways of doing
semantic composition.  Are there ways that are problematic for some reason?
Is it a question of constraining the space of possible grammars (e.g. for
learnability concerns)?  Related to issues of incremental processing?


>
>> 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).
>
>
Oh, I missed that in the paper.  So are we then talking about
"interpretation"
because the fully scoped MRSs are assumed to have interpretations via
a second layer of modeling?


>   (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.
>
>
Got it.


>  (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.
>
>
In the spirit of keeping the discussion going without delays, I haven't
actually
played with this yet.  But: accessible from the trees seems to suggest that
the
testing takes place over particular analyses of particular inputs, and not
directly
on the grammar as static code analysis.  Is that right?

Thanks again,
Emily



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