On 12/15/10 2:50 PM, Matthew West wrote:
> [reposted here as requested by Peter]
>
> Dear Ian,
>
>> I'm constantly amazed at the passion that OWL seems to arouse.
> I am surprised at the strength and vigour of John's objections too, but I
> think you are missing some of what is objected to.
>
>> OWL and the OWL
>> 2 profiles are simply fragments of FOL with useful computational
> properties.
>> I'm surprised that we can get so excited about decidable fragments. I'm
> even
>> more surprised that someone who apparently likes FOL "hates" these
> particular
>> fragments.
> MW: Well if OWL was just an abstract syntax for these fragments I doubt if
> anyone would be half as excited. What I think causes a collective groan
> amongst those that have been around for several decades in this space is the
> XML implementation on top of RDF. It is like inventing a square wheel when
> you have a round one sitting in the corner (SQL) and then layering something
> uncomfortably on top of it. (01)
Matt, (02)
Syntax / Model conflation is a global problem in the Semantic Web
universe of discourse, sadly. (03)
There is nothing about OWL that is XML specific. Its a FOL strand. (04)
If only we could just get RDF/XML distraction out of the way. if only we
could somehow just pull that off re. Linked Data and broader Semantic
Web discourse. (05)
I am increasing inclined to believe that many who speak in terms of a
Syntactic vs Semantic Web dichotomy, still actually act Syntactically
most of the time e.g. a lot Linked Data and broader Semantic Web
commentary ultimately boils down to covertly conflating everything with
RDF syntax. (06)
OWL != RDF . (07)
RDF != Linked Data :-) (08)
....... (09)
Kingsley (010)
>
> Regards
>
> Matthew West
> Information Junction
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>
>
>> I can easily understand why you and others might believe that OWL is too
>> restricted for what you want to do, and why you might want to use full
> FOL.
>> Please go right ahead -- I won't be in the least offended. I don't see how
> OWL
>> would interfere with such an endeavour, and I would have thought that it
> might
>> even help as you can trivially extend OWL ontologies with arbitrary FO
> axioms.
>> In fact, you could think of OWL as being a design pattern, which you
>> apparently like, as opposed to a fragment, which you don't like.
>>
>> Regarding the other techniques you mention, it is true that they can be
> used
>> to address some of the problems associated with computational complexity
>> (where we can think of semi-decidability as being a very high complexity
>> class). Modern OWL reasoners already employ many of these techniques. Of
>> course we can, by definition, never "deal with" these problems, and
> ontology
>> languages with high computational complexity will always suffer from some
> lack
>> of robustness, i.e., relatively small changes in the ontology and/or data
> may
>> result in performance "falling off a cliff". This was the motivation for
> the
>> definition of the various OWl profiles: if a given application requires
> some
>> guarantee of robustness, then they can obtain it by staying within a
> suitable
>> profile. Note that the syntactic definition of profiles is crucial here,
>> otherwise one risks deciding membership of the profile being an
> intractable
>> problem in itself.
>>
>> Coming back to the OWL -v- FOL question, I think that much of the
> "problem"
>> arises from fundamental differences in how we view the design and use of
>> ontologies. Many of the ontologies I see are extremely simple (in fact I
> often
>> find myself being asked to defend the unnecessary expressive power of OWL)
> and
>> perhaps wouldn't pass muster if examined by a formal ontologist. However,
> they
>> may still be found to be an extremely useful piece of an application, even
> if
>> only a rather small piece. I tend to see this in a positive light -- we
> are
>> raising the profile of and exploring applications for ontologies.
> Hopefully
>> you can try to see OWL in a similar light -- it is raising the profile of
>> ontologies, encouraging the use of (a fragment of) FOL as an ontology
>> language, and providing you with a ready source of "customers" ripe for
>> "upgrading".
>>
>> Regards,
>> Ian
>>
>>
>>
>>
>>
>> On 10 Dec 2010, at 10:57, John F. Sowa wrote:
>>
>>> Ian,
>>>
>>> Before saying anything else, let me emphasize that I believe the work
>>> on algorithms, complexity, and decidability by you and your colleagues
>>> is very high quality and very important for computer science.
>>>
>>> But the sentences at the end of your note explain why *I hate OWL* :
>>>
>>>> In fact, it can be shown that query answering in OWL 2 RL [Rule
> Language]
>>>> is possible in time that in the worst case increases only polynomially
>>>> with the size of the data. In *this* sense, OWL 2 RL really is less
>>>> (computationally) complex. However, as I mentioned above, the price
>>>> users pay for this is an *increase* in syntactic or cognitive
> complexity.
>>> By syntactic complexity, I realize that you are talking about something
>>> much more fundamental (and cognitively much harder for people to learn)
>>> than the angle brackets. But knowledge acquisition has always been
>>> the major bottleneck in AI and the SW. Anything that increases the
>>> "cognitive complexity" is a bad step in the wrong direction.
>>>
>>> As Dean said,
>>>
>>>> I find that in the classes I do teach, the students are very concerned
>>>> about complexity in the computational sense...
>>> But there are many ways of dealing with computational complexity while
>>> actually *reducing* the cognitive complexity:
>>>
>>> 1. Design patterns. Every programming language is undecidable, but no
>>> programmer would ever ask for less expressive power. Instead, they
>>> have developed *design patterns* for systematic ways of using their
>>> languages in ways that are known to be safe and efficient.
>>>
>>> 2. Hybrid systems. The original DLs were packaged as hybrids with
>>> the DL component designed for efficient classification and a more
>>> expressive language (rule-based, full FOL, or even arbitrary
>>> procedures) were used to achieve the required expressive power.
>>> And design patterns (or something similar) can be used for the
>>> more expressive part of the hybrid. (The RL option of OWL doesn't
>>> address the main reason why people use hybrids: they need more
>>> expressive power, not less.)
>>>
>>> 3. Dynamic algorithm selection. Cyc has developed the largest formal
>>> ontology on the planet, but CycL imposes no restrictions on the
>>> expressive power. Instead, they use dynamic methods for selecting
>>> appropriate algorithm(s) for each problem or subproblem they
>>> encounter. Similar strategies are also used for the systems that
>>> compete on the Thousands of Problems for Theorem Provers (tptp.org).
>>>
>>> 4. Knowledge compilers. For many applications, it's possible to do
>>> a *static* selection of the algorithms: Map the very expressive
>>> languages (such as CycL and others) via appropriate design patterns
>>> to forms can be processed efficiently by known algorithms.
>>>
>>> I'm sure that you know the references for these methods, but for
>>> other readers, I include some in the following article:
>>>
>>> http://www.jfsowa.com/pubs/fflogic.pdf
>>> Fads and Fallacies About Logic
>>>
>>> At the ICCS 2010 conference, Boris Motik gave a good presentation
>>> about adding finite graph models to OWL in order to broaden its
>>> expressive power while preserving decidability.
>>>
>>> I certainly like the idea of supporting graphs, but not the idea
>>> of adding more cognitive complexity to an already overstuffed
>>> language. Instead of stuffing more into OWL, why don't you ask
>>> some of your students to do research on methods such as #1 to #4
>>> above to find ways of *reducing* the cognitive complexity?
>>>
>>> Other talks at ICCS described more efficient algorithms for
>>> Formal Concept Analysis (FCA), which generates consistent lattices
>>> from source data that is cognitively extremely simple.
>>>
>>> That would be another excellent topic for your students: design
>>> hybrid systems that combine an FCA-style of hierarchy with automated
>>> or semi-automated methods for supporting additional expressive power
>>> at varying levels of complexity up to the level of CycL.
>>>
>>> Cognitive complexity is killing the Semantic Web. As a result,
>>> people are building their own hybrids that add very scruffy methods
>>> to OWL or RDFS or RDFa -- thereby destroying the decidability that
>>> the OWL restrictions were designed to support.
>>>
>>> The four techniques above (or something similar) would be an
>>> excellent way to support Tim B-L's project for "Web Science".
>>>
>>> John
>>>
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> (011)
-- (012)
Regards, (013)
Kingsley Idehen
President& CEO
OpenLink Software
Web: http://www.openlinksw.com
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