Re: [ontolog-forum] Requirements of computer language semantics

[Adrian Walker <adriandwalker@xxxxxxxxx>]

Hi John --

You wrote 

   Other things being equal, it makes more sense to try
    to map a new language L1 to some previously defined
    and analyzed language than to try to define the
    semantics for L1 from scratch.

Actually, you can just construct a model theory for L1 directly.  This may of course lead you to modify L1.  But when the model theory is done, you can use it as a gold standard for implementing a reasoner.  That's way easier and less error prone than trying to do the same kind of thing via L1---> L2.  It saves you having to prove the correctness of the --->.   It also gets rid of a layer of interpretation or compilation at run time.

               Cheers,  -- Adrian

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Adrian Walker
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On Wed, Mar 18, 2009 at 8:02 PM, John F. Sowa <sowa@xxxxxxxxxxx> wrote:

Chris,

I agree with the technical points you made, but the judgment
about what makes "more sense" is debatable:

CM> Other things being equal, it makes a great deal more sense
 > to provide a semantics for L1 directly [than to define the
 > semantics by translation to a previously defined language L2].

Interoperability is always a major practical concern in comp. sci.,
and a translation from a new language L1 to a previously defined
and analyzed language L2 can help answer many important questions:

 1. Are they logically equivalent or can one be mapped to a subset
    of the other?

 2. If the answer to #1 is no, then is there some subset L1' of L1
    and L2' of L2 such that L1' and L2' are logically equivalent?
    Are those subsets L1' and L2' big enough to be useful?

 3. Which reasoning engines already available for L2 can be
    be used for L1 or some subset of L1?

If the model theory of L2 is defined independently of L1, it is
much harder to answer these questions.

For a previously unanalyzed language such as mKR, many of us
have little or no confidence in its consistency.  It's quite
possible that if Dick (or one of his colleagues) tried to
map mKR expressions to a previously defined language, they
might encounter some serious difficulties.  Therefore, they
might choose to redefine the troublesome features of mKR
in a way that simplifies the translation.

So I would argue for the following procedure:

   Other things being equal, it makes more sense to try
   to map a new language L1 to some previously defined
   and analyzed language than to try to define the
   semantics for L1 from scratch.

John

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