Re: [ontolog-forum] Knowledge graphs by Google and Facebook

[William Frank <williamf.frank@xxxxxxxxx>]

On Mon, Jan 21, 2013 at 12:04 AM, John F Sowa <sowa@xxxxxxxxxxx> wrote:

Kingsley and Len,

I want to emphasize that theoretical issues and practical issues are
*both* important.  The best combination is to have developers who
understand both theory and practice.

....

 

LY
> I disagree with characterization of *semantics* of SQL as purely
> theoretical issue with no significant practical implications...

As I said, theory and practice are both important.  In any case,
there are many, many different combinations of notations, logical
expressiveness, and storage methods that have different kinds of
tradeoffs for different kinds of applications.

The worst policy is to make decisions based on one-line slogans
about complicated issues such as decidability, expressive power,
notations, storage methods, CWA, OWA, etc.

Yes! tying theory and practice.

I was so hoping this conversation would wander in this direction, to help me out in understanding the underlying issues.   

Is it not possible that the CWA is only one of many semantic models for SQL, rather than being THE semantics for SQL?. 

Matters of completeness, decidability, and such, of a logic implicit in a language etc. are about the *inference system* and its *relationship* to the semantics, so different semantics might yield interestingly different results, or the same results, also interesting.   For example, I can imagine a multi-valued logic yielding more realistic results,and someone comparing these semantics

Is it not desirable to consider these matters in conjunction with expressive power, so that if we find that the desirability of of using a language and deductive system for machine processing has a limited semantics, we will note this fact, when tying our work on these languages to ***practice***?  

Tying theory to practice is the key, and when I see what seems like complacency over theoretical results that need special attention to make them used appropriately, and answers to questions about the tie that are just more theory, it makes me nervous.

So, this is what I think I have learned from this discussion, that I can apply:

"The only known semantics that makes SQL and many other computer-usable (for the things we want computers to do) -languages work is something called the "Closed World Assumption".   This so-called "assumption" is in fact obviously false, so when we go about using the the results of queries in our programs and interpreting them as people, we need to be very careful to take this weakness of the computer languages into account.  The Closed World "Assumption" is contrasted with the Open World "Assumption," which is also not an assumption, but a fundamental tenant of science and aspect of human experience.   This open world tenant seems often forgotten by many people in applied sciences, anywhere from software engineering to medicine. 

Thanks to all.

Wm
 

John

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-- 
William Frank

413/376-8167


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