Ron Wheeler wrote:
> On 31/07/2010 11:54 AM, Mike Bennett wrote:
>
>> One thing I would add to that (taking it in a different direction), is
>> that for some of the reasons that one might use OWL or Common Logic,
>> decidability is not even an issue. This is in formally recording and
>> defining business facts. Rather than having modelers design a logical
>> model from whatever they grasp of the business reality (while their
>> personal grasp of those facts remains undocumented), more firms should
>> really be pushing for a formal record of the business knowledge against
>> which designers design their stuff - this is part and parcel of ordinary
>> mature development methodology. In this context, the semantic model is
>> never going to be reasoned over or used as an application in its own
>> right, it's simply the hitherto missing record of how the business sees
>> the facts that the data will be about.
>>
>> To achieve that end, one simply needs a suitably formal way of
>> expressing real things and real facts about those things, under a simple
>> and explainable theory of meaning (such as set theory, for OWL). So this
>> is a good reason to use OWL (or other CL languages) which has nothing to
>> do with the considerations addressed here.
>>
>> Maybe I'm stating the obvious but I think it's worth keeping in mind.
>>
>
> I think that these comments are very good to see from time to time to
> keep the conversations a bit grounded in reality.
>
> At least, I appreciated it.
> It reminds those in pursuit of theoretical perfection that many others
> are in search of solutions to real problems where attainable results
> with imperfect solutions will sometimes be the best outcome for the client.
>
> Ron
>
>> Mike
>>
>>
sowa@xxxxxxxxxxx wrote:
>>
>>> Cameron, Ian, et al.,
>>>
>>>
>>>
>>>> Wouldn't Common Logic be the
>>>>
>>>>
>>> "logical" choice if one were to
>>>
>>>
>>>> relinquish
>>>>
>>>>
>>> decidability? It's an ISO standard and tools are gradually
>>>
>>> starting to appear.
>>>
>>>
>>>
>>>>> OWL and CycL are not really
>>>>>
>>>>>
>>> comparable, because OWL is based on a
>>>
>>>
>>>>> fragment of First
>>>>>
>>>>>
>>> Order Logic that is known to be decidable, for which
>>>
>>> provably correct reasoning algorithms are known and for which effective
>>>
>>>
>>>
>>>>> implementations based on said algorithms are available.
>>>>>
>>>>>
>>> OWL's expressive
>>>
>>>
>>>>> power could, of course, be easily (indeed
>>>>>
>>>>>
>>> arbitrarily) extended if one
>>>
>>>
>>>>> were prepared to compromise on
>>>>>
>>>>>
>>> some or all of these design constraints...
>>> I am on my way home from
>>> Malaysia, where three collocated conferences discussed these and other
>>> issues: MJCAI (Malaysia Joint Conference on AI), ICCS (International
>>> Conference on Conceptual Structures), and STAKE (Semantic Technology And
>>> Knowledge Engineering).
>>> One of the invited speakers, Boris Motik,
>>> wrote his PhD dissertation on DLs, and he is now teaching at Oxford. He
>>> made the observation that the desire to enforce decidable models led to
>>> many dubious compromises, such as the limitation to tree-structured
>>> models. Unfortunately, such models cannot represent any structures that
>>> contain cycles.
>>> One example would be a benzene ring. You can
>>> represent a structure with 6 carbon atoms, but you can't say that the
>>> sixth atom is connected to the first because that would create a cycle.
>>> Instead of describing just one fixed intended model, a typical OWL
>>> description would have a huge number of models. (There are ways of
>>> getting around such restrictions, but they involve jumping through lots of
>>> hoops with a large number of complex conditions to state something very
>>> simple.)
>>> As another example, Botik showed a simple OWL description
>>> of the human heart. Unfortunately, that description had an infinity of
>>> models. One model had exactly one left ventricle (which most people
>>> have). But other models could have any number of left ventricles. There
>>> was no way to limit the intended models to those that have just one left
>>> ventricle.
>>> As a solution, Botik proposed an extension to OWL that
>>> allowed arbitrary finite graphs, which could contain cycles. As a
>>> convenient notation for that extension, he drew diagrams that looked very
>>> much like simple (non-nested) conceptual graphs.
>>> OWL should
>>> be considered an open-ended family of languages, starting with OWL full,
>>> OWL lite, OWL DL, OWL 2.0, SWRL, OWL-Graph, etc., etc., etc.
>>> These
>>> versions of OWL have only two things in common: the three letters O-W-L
>>> in their name, and the fact that every one of them is a dialect of Common
>>> Logic.
>>> Since this thread is also addressing CycL, we should point
>>> out that CycL could also be considered a dialect of Common Logic. CycL
>>> and CL are very easily comparable to OWL: They are supersets of all the
>>> OWL versions and they can be used to relate each and every one of them.
>>> That is a very useful property.
>>> As for undecidability, it is an
>>> interesting theoretical property. But Lenat and other Cyclers have
>>> observed that in the 26 years of Cyc, undecidability has never caused any
>>> serious problems for any practical application.
>>> Occasionally, a
>>> collection of Cyc axioms might cause one of their inference engines to get
>>> hung up in a loop. That is also true of every major programming
>>> language. Java, C, Fortran, etc. are all undecidable, and nobody
>>> cares. Programmers use methods of structured programming and design
>>> patterns that enable them to predict when they have safe programs, and
>>> they have a very large number of guidelines for ways of avoiding the
>>> infinite loops.
>>> If anyone asks how many tools are available for
>>> Common Logic, the short answer is the sum total of all the tools written
>>> for any and every dialect of Common Logic. That includes all the Semantic
>>> Web languages, all the theorem provers used for
tptp.org, and huge numbers
>>> of experimental and commercial tools available today. Among other things,
>>> Common Logic has been used to define the semantics of the UML diagrams
>>> (check Google for fUML or formal UML). So all of the UML diagrams can be
>>> considered dialects of Common Logic, and all the UML tools can be
>>> considered CL tools.
>>> The advantage of CL is the ability to relate
>>> anything stated in any of those languages to any other language. Very few
>>> logics have that property.
>>> When I get back home, I'll send more info
>>> with references to the details.
>>> John
>>>
>>>
>>>
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