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Re: AW: [ontolog-forum] Current Semantic Web Layer Cake

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 3 Aug 2007 10:59:52 -0500
Message-Id: <p06230905c2d7f2e1a430@[10.100.0.67]>
To: "Valentin Zacharias" <Zacharias@fzi.de>
Cc: "Pat Hayes" <phayes@ihmc.us>, "John F. Sowa" <sowa@bestweb.net>, "[ontolog-forum]" <ontolog-forum@ontolog.cim3.net>, "Ivan Herman" <ivan@w3.org>, "Juan Sequeda" <juanfederico@gmail.com>, "SW-forum list" <semantic-web@w3.org>

>Hi!
>
>Pat Hayes said:
>[...]
>>I am slightly concerned that this peculiar kink in the layer
>>cake has been put there deliberately to make it possible to do an
>>end-run around a unifying logic. Which when one takes into account
>>the whole point of "Unifying", would IMO be a pity.
>[...]
>
>I can understand that people insist on Semantic Web languages to have a
>formal, or even a model theoretic semantic.

"even" ?? But never mind, let us proceed.

>What I don't get is that you
>(and John F. Sowa in other emails) seem to insist that this must be classic,
>FOL like, monotonic semantic and that all formalisms with different
>semantics (or kinds of reasonings) have no place in the Semantic Web.

You draw too rapid a conclusion. I don't think 
that nonclassical logics have NO place on the 
SWeb. But one has to draw a distinction between 
'useful somewhere' and 'suitable as a basis for 
global interoperability'. All of the Sweb 
standards defined so far (RDF, OWL, SPARQL) are 
intended for use at the 'top level' of the SWeb, 
to be suitable for use for communication between 
systems located anywhere on the Web, using data 
which may come from many sources, be archived or 
not, etc.. Under these assumptions one can make a 
very good argument that the basic semantics of 
such interoperation languages must be monotonic, 
context-independent: because, in essence, the 
context in which it was published is no longer 
available at the point of use. See 
http://www.ihmc.us:16080/users/phayes/IKL/GUIDE/GUIDE.html#LogicForInt
and
http://ontolog.cim3.net/file/resource/presentation/PatHayes_20061026/OntologyWorkshopSlides.html 
especially slides 4-6

>To me it seems obvious that these semantics cannot be the exclusive basis
>for reasoning on a global,open knowledge based system

Not exclusive, but for the main basis, I think 
one cannot really go much beyond classical 
semantics, precisely because they are so weak. 
All other semantics make some implicit assumption 
which is not globally valid.

>, because:
>
>1) These semantics do not consider

True. But the fact that they do not consider 
certain topics does not mean that those topics 
are incompatible with them, or are ruled out of 
consideration for ever. And one should not 
usually seek to standardize topics which are 
still the subject of active research discussion 
and have no body of established practice to 
appeal to.

>quantitative aspects (e.g. 5000 locations
>state that a(mike), only 2 state that b(mike)), don't allow for closed world
>reasoning

They ALLOW for it, but do not mandate it during 
global information exchange, for the very good 
reason that the Web is not a closed world. CW 
reasoning is simply invalid when applied to the 
entire Web. The unique name assumption is false; 
failure is not negation; etc..

>, do not consider trust, require very strict global consistency....

Again, they do not REQUIRE global consistency, or 
indeed even local consistency. They simply, as 
classical semantics always do, give up when faced 
with inconsistency. They do not deal adequately 
with it, true: there is as yet no globally 
acceptable standard way to deal with it. One has 
to deal with each case on its merits. The fact 
that the standards do not deal with these issues 
is not a message that they are irrelevant or 
prohibited, only that they are still the subject 
of research and to some extent emergent future 
practice. We will have to wait and see what 
happens, before trying to impose a standard here.

>Because of this they cannot reflect the intuitions and expectations of
>humans about what should be concluded from a set of statements as unordered
>and ungoverned as the web.

I think you are muddling the chaotic state of the 
Web with the idea that information on the Web 
must be somehow faulty or inconsistent, or that 
people use (or perhaps should use) a different 
kind of reasoning when faced with a large messy 
dataset. I don't think this is a valid 
conclusion. Tim B-L has some interesting musings 
on this topic, by the way.

>  Hence actual applications will in any case use
>other notions of truth and entailment (or come to conclusions that are not
>accepted by the users and probably not very useful).*

What makes you assume that contexts and 
uncertainty reasoning are excluded by a classical 
semantics?

>2) Should we really ever get reasoning semantic web agents, isn't it
>preposterous to assume that will rely exclusively on logical deduction?

Perhaps not exclusively, but I think the main 
basic inference mode will be deductive, yes. That 
has certainly been the case so far in most 
applications. Classical deduction can, with 
current technology, be usefully applied to 
datasets containing many millions of facts.

>- Why
>not induction, abduction, analog reasoning, data mining, nlp, ir, simulation

You are muddling together a host of unrelated 
topics here. Induction and abduction are not even 
logical forms of entailment, and are both 
consistent with a classical notion of truth. 
Analogical (aka metaphorical) reasoning turns out 
in most application I have seen to be a 
pattern-matching process on structures which 
themselves have a classical semantics (and in 
many cases are expressions in FOL.) Data mining 
is a separate topic which is not required to be 
nonclassical (we have used datamining software 
with OWL, for example). NLP systems often use 
deductive reasoning. And so on. Yes, Im sure all 
these and more will be used by SWeb technologies 
of one kind or another. None of that however is a 
good reason for basing the global notations of 
information exchange on anything more elaborate 
than simple model theory.

>... Doesn't this mean that in any case there will never be a complete
>mapping between the "proof" and the "logic" layer (as currently envisioned)?
>I also don't see how any kind of inference can be done on web scale without
>a large (essentially heuristic) information retrieval component trying to
>get the relevant statements (considering what we know about the complexity
>of inference algorithms) - again breaking the direct logic layer-proof layer
>mapping.
>
>my opinion in short: we don't have any semantics that covers everything that
>is needed (and I don't even see one at the horizon), hence we should not
>stifle innovation by insisting on one thats clearly inadequate for the task
>at hand.

I agree with your premis, but draw a totally 
different conclusion. As we MUST have an 
interoperability standard to even get the SWeb 
off the ground, we should choose one that 
restricts innovation as little as possible: the 
most bland, vanilla, uncontroversial basis that 
everyone can accept and build on. What semantic 
framework would you suggest be adopted as the 
basis for SWeb information exchange?

(BTW, I find your criticism kind of ironic, since 
we have been the subject of torrents of criticism 
for making the RDF and OWL-Full semantics too 
'non-standard' by not basing it strictly on 
textbook model theory.)

Pat



>
>
>cu
>
>valentin
>
>
>*: given the large amount of research into things like circumscription,
>uncertainty reasoning, rdf/dl+contexts etc. I was under the impression that
>this is a SW-community mainstream position.
>
>--
>email: zacharias@fzi.de
>phone: +49-721-9654-806
>fax  : +49-721-9654-807
>http://www.vzach.de/blog
>
>=======================================================================
>FZI  Forschungszentrum Informatik an der Universität Karlsruhe (TH)
>Haid-und-Neu-Str. 10-14, 76131 Deutschland, http://www.fzi.de
>SdbR, Az: 14-0563.1 Regierungspräsidium Karlsruhe
>Vorstand: Rüdiger Dillmann, Michael Flor, Jivka Ovtcharova, Rudi Studer
>Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
>=======================================================================
>
>>  -----Ursprüngliche Nachricht-----
>>  Von: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org]
>>  Im Auftrag von Pat Hayes
>>  Gesendet: Dienstag, 31. Juli 2007 17:20
>>  An: John F. Sowa
>>  Cc: [ontolog-forum]; Ivan Herman; Juan Sequeda; SW-forum list;
>>  semantic_web@googlegroups.com
>>  Betreff: Re: [ontolog-forum] Current Semantic Web Layer Cake
>>
>>
>>  >Pat,
>>  >
>>  >I agree that the proof box is misplaced, but I think
>  > >that the major problem is that the logic box is not
>>  >correctly positioned.
>>  >
>>  >>  http://www.w3.org/2007/03/layerCake.png
>>  >
>>  >PH> Hmm, I wonder why the 'Proof' Tetris piece has
>>  >>  a connection to Rule without going through Unifying
>>  >>  Logic.  That seems like a very bad decision to me
>>  >
>>  >Unifying Logic is the framework that includes the others
>>  >as subsets:  RDF, RDF-S, Rule RIF, OWL, and SPARQL.
>>  >
>>  >Each of these subsets is tailored for a specific kind of
>>  >inference engine and/or a specific range of uses.  What
>>  >unifies them is the common model-theoretic semantics.
>>  >That semantics enables all of them to interoperate on
>>  >shared data and produce consistent results.
>>
>>  Thats what I would expect, yes. And I know the overall picture. What
>>  surprised me was the fact that there seems to be a special
>>  short-circuit allowing Rules to connect to Proof without taking the
>>  Logic into account. Which in turn suggests a special dispensation for
>>  Rules to avoid having to have a common semantics with everything
>>  else. As I know there are, as the popular media says, Powerful Forces
>>  in the Rules meta-community which would approve of short-circuiting
>>  conventional semantics altogether in favor of, say, some version of
>>  Prolog, I am slightly concerned that this peculiar kink in the layer
>>  cake has been put there deliberately to make it possible to do an
>>  end-run around a unifying logic. Which when one takes into account
>>  the whole point of "Unifying", would IMO be a pity.
>>
>>  Pat
>>
>>  >
>>  >My suggestion would be to draw the Unifying Logic box as
>>  >a large container that includes all the others inside:
>>  >RDF, RDF-S, Rule RIF, OWL, and SPARQL.
>>
>>  The layer-cake display has become a kind of W3C icon now.
>>
>>
>>  --
>>  ---------------------------------------------------------------------
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>>


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Received on Friday, 3 August 2007 16:00:13 GMT

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