[SCL] Metalinguistic constructs

[Christopher Menzel]

Hi Tanel, thanks for your reply.  I fear perhaps I came off sounding 
somewhat confrontational in my previous response, which was not my 
intent.  You raise important issues about the nature and direction of 
the project, and I am quite open to considering all of them.  My plea 
-- arising in part because the speed at which ideas appear to issue 
from your fingertips! -- was only that we have a very clear statement 
of our aims so that we can be reasonably sure that we are pursuing them 
and not venturing off into new territory.  I believe Pat is in the 
process of formulating a draft of such a statement as we speak, er, 
type.

As to more specific comments:

On Tuesday, December 24, 2002, at 05:06 AM, Tanel Tammet wrote:

> Hi,
>
> Christopher Menzel wrote:
>> On Saturday, December 21, 2002, at 04:31 AM, Tanel Tammet wrote:
>>>   I'd prefer viewing SCL as a vehicle where we can convey data in
>>>   various logical languages: FOL, intuitionistic logic, TR, default
>>>   logic, etc.
>> Well, then we might have a disagreement over what SCL is about.  My 
>> understanding, in Pat's words, is that its purpose is to be "a good 
>> logic standard."  More specifically, he wrote:
>>
>>   I propose to form an ad-hoc working group whose aim will be to 
>> produce a firm,
>>   detailed CL-style standard suitable for immediate application, with 
>> similar aims
>>   to the declared CL project, ie a general-purpose first-order logic 
>> language, with
>>   a clear semantic theory and a machine-oriented syntax...
>>
>> By contrast, I'm not exactly sure what a vehicle for conveying data 
>> data in various logical languages is supposed to be, but it doesn't 
>> sound like something that is *itself* a logic.  But if we *are* 
>> working on something that is itself a logic, then if we want it 
>> *also* to be able to convey data in various other logics (and it 
>> isn't obvious to me that that is what we want -- though it isn't 
>> obvious to me that it isn't either), then what we need is a logical 
>> *theory* of those other frameworks and how data in them is conveyed.  
>> That will, of course, involve the sort of extension indicated above.  
>> Note this is not simply my idea; it has been a part of the KIF/CL 
>> group for quite some time -- though not with quite the scope you seem 
>> to have in mind.  Now maybe it wasn't good idea for some reason we 
>> might convince ourselves of, but I think we should be careful about a 
>> sudden change of direction.
>
> I agree that our group should not wander into uncharted territories
> we did not plan to visit.

That's putting things a bit more strongly than I was trying to suggest. 
  As I suggest above, it could be that we SHOULD wander into hitherto 
unplanned territories.  We just need to be explicit about doing so.  
Given Pat's initial, brief description, it wasn't clear to me how to 
reconcile the project with some of the many interesting and important 
ideas you have raised.

> Since my only knowledge of the CL project comes from reading
> the drafts, minutes (and the earlier KIF stuff) I may well
> have had ignored some agreements of the CL project.
>
> Pointing this out is a right thing to do, thanks!

Good -- as is exploring possible revisions and extensions to the 
project!

> Despite of this, I still think that it would be very
> useful if we could achieve some of the goals I put
> into the mini-agenda before. It would very good if
> we could stick to the CL goals, yet achieve something
> additional on a way.

I STRONGLY AGREE with this.

> I really think that SIMPLY agreeing on a common
> syntax of FOL does not bring many benefits and is
> not necessarily an important goal in itself
> We already have a number of FOL syntaxes. If we simply
> wanted a nice FOL syntax, then why not take some
> classical syntax directly from the classical books :-)

Granted -- but you are only talking about the basic foundation of the 
project.  It has always been part of KIF/CL to add clear mechanisms for 
enabling integration across difference representational frameworks.  
Among the issues you raise, at least implicitly, is whether to rethink 
the "metalinguistic" approach we have had in mind.  (I still think this 
approach is both practically and theoretically necessary, but much of 
the apparatus could be presented in a more convenient form to users 
along the lines you suggest.)

> Exchanging pure FOL formulas between the systems without
> any agreed-upon possibility to give metainformation
> is not of much use. Metainformation, as the examples pointed
> out, is really crucial in practice. If we cannot convey
> it, then obviously system implementors need to design
> their own languages for that. During this, the considerations
> stemming from the need to exchange metainformation might
> well make them to decide to drop the pure FOL standard
> we or CL had created.

The expression of metainformation has also been an important goal of 
CL, though it unfortunately has not made it into much of the available, 
and quite sparse, documentation.  It has mostly been discussed in group 
meetings, though you'll find some email discussions in the KIF archives 
as well.  It is definitely critical, though, and should be at the 
forefront of the issues we take up in SCL.

> Similar considerations apply to conveying information
> in other logics. People have a very strong tendency
> to use exotic logics here and there. Very often
> these logics are extensions or special forms of FOL,
> or share large parts with FOL. If we make it possible
> for them to use our syntax, they will not have to devise
> completely different syntaxes and the common FOL
> part in their formulas would be understandable to
> "ordinary" systems as well. FOL would be a distinguished
> common denominator, so to say, not a "not-invented-here"
> system to be avoided.

Again I agree, though we are into dicier territory when we start 
conveying information about other logics, not just other languages -- 
which only means we have work to do!

> To summarize what I learned from your message:
> it is highly desirable to view the metainformation
> constructions as FOL formulas.

Let me qualify that -- there should be a way to translate the construct 
you suggest into a completely kosher FOL form.  The convenient syntax 
you suggest could then be recommended as the "presentation" syntax for 
actual users.

> Although I think this will not be easy, we may try.

I am more sanguine than you on this point (though we do not as yet 
really have a precise formulation of what that point is -- perhaps when 
we do we will be of one mind).

Highest regards,

-chris

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