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Re: [ontolog-forum] Webby objects

To: edbark@xxxxxxxx, "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Amanda Vizedom <amanda.vizedom@xxxxxxxxx>
Date: Mon, 19 Nov 2012 14:33:28 -0500
Message-id: <CAEmngXvF+tc0LgY+p2gnYuatk=r3Az06CMuTfoX6+Fn7QUPJXg@xxxxxxxxxxxxxx>
Ed and All,

I'd like to point out, and emphasize, that whether customers find undecidability / the throwing up of hands acceptable depends very much on how the question is put to them. If abstracted from context and meaningful comparison (where "meaningful" = presented in terms of trade-offs related to customer requirements and desiderata), it sounds scary and no one wants it. But with a  little bit of real explanation thrown in, things change.

In particular, the "decidability" of a language is only a guarantee of an answer within a finite amount of time.  This is not a substantial or useful guarantee in a used system. *Any* usable, fielded system will have to have some way of throwing up its hands, some threshold at which it will throw up its hands, rather than waiting for a guaranteed finite-time result. So, decidability does not get one out of this bit of theoretical inelegance..

The *real* choice of what is acceptable is never "will halt in a finite amount of time" and "may not halt in a finite amount of time." because the former itself is not good enough for application and deployment. 

The real valuable work comes from identifying logic languages and procedures, that maximize expressiveness, usability, and reasoning within the domain of statements and tasks the user needs. That is more complex and subtle. There are lots of ways to design systems to either disallow certain statements (IMHO, better done semantically than via unusably counter-intuitive or restricted syntax), or decline to process certain reasoning patters that have a high rabbit-hole risk, or cut out after a certain time, or use other techniques to tune performance. The line between decidable and undecidable systems is not a sweet spot for this.

For all of these reasons, IMHO, decidability is a red herring. Worse, and to mix my metaphors, it is a red herring that has led far too many talented people on a wild goose chase when they could be doing much more useful work to advance the state of the science and technology in really valuable ways.



On Mon, Nov 19, 2012 at 1:52 PM, Ed Barkmeyer <edbark@xxxxxxxx> wrote:

Everyone agrees that FOL is more expressive and potentially more useful,
but all of the reasoning procedures that are widely used in academia
either restrict the allowable FOL inputs in some way that greatly
reduces its expressiveness or are programmed to throw up their hands at
some point -- they "halt" by saying "not determinable" (in some
language).  The problem of not knowing the relationship between input
data -- the sets of valid sentences -- and the "not determinable" result
is what causes industry to shy away from FOL reasoners.

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