W3C home > Mailing lists > Public > semantic-web@w3.org > August 2007

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

From: Valentin Zacharias <Zacharias@fzi.de>
Date: Sat, 4 Aug 2007 20:44:42 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A03737C9@judith.fzi.de>
To: "Pat Hayes" <phayes@ihmc.us>
Cc: "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 !

Thank you for your elaborate reply! 
I'm afraid that the point I was trying to make is getting lost in the
discussion, so I do not answer to all your statements point by point but try
to rephrase the discussion.

The starting point was whether the "proof" layer needs to be exclusively
based on unified (FO)logic - something I saw being implied by your objection
to the direct connection between the "Rule/RIF" and "Proof Layer"in the
layer stack - bypassing the unified logic.  Considering that I understand
the proof layer to contain *all* SWeb reasoning I feared that this also
meant that the proof layer must exclusively rely on OWL  deduction -
something that struck me as utterly unrealistic (and that's also where the
long list of "muddled, unrelated topics" came from - things beyond OWL
deduction I imagine happening in the proof layer). 

Now I understood your reply as meaning that for you the OWL semantics are a
kind of minimalistic, basic semantics; that people are free to use other
kinds of assumptions and reasoning on top, kind of at their own risk.  Also
that you imagine this to be mainly logical deduction and that many of the
features under discussion to be used  there are just not good enough
understood to be standartized yet.

Then, to come back to the starting point, we do not have a clear picture of
everything happening in the proof layer - and we could imagine things in the
proof layer not (exclusively) being based on OWL semantics. But then I don't
get your problem with the "rule-layer <-> proof-layer kink in the layer
cake. Yes - one unified logic has a certain beauty to it - but there is no
problem with some SWeb agent taking some statements, using some ontology to
derive some more and then using some PROLOG rules and a query to get its
final result - or is there? Yes, depending on the order in which i do this
and details of the formalisms the conclusions may not be correct FOL
inferences - but then, didn't we agree that lots of the things in the proof
layer won't be?  To me it seems that the moment you are insisting on the
proof layer to be based exclusively on the Unified Logic (equated with FOL
semantics) your minimalistic semantics that keeps all possiblities open,
suddenly excludes quite a lot (the LP community for one). 

and to answer one more point:
>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, [...]
> Tim B-L has some interesting musings 
> on this topic, by the way.

It is indeed my conviction that information on the web will always be faulty
and inconsistent - I fail to see any argument to the contrary; even cyc
failed to build one consistent world-kb - and this is still a relatively
small kb, build under very controlled circumstances by very skilled people
with largely aligned goals and relatively similar cultural background and
education. Wikipedia is permanently faulty and inconsistent - as is the
Encyclopedia Britannica or every humans knowledge.  But I'll read up on Tim
B-Ls musings on the topic -  I assume you are referring to the later
chapters of "Weaving the web"?



email: zacharias@fzi.de
phone: +49-721-9654-806
fax  : +49-721-9654-807

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: Pat Hayes [mailto:phayes@ihmc.us]
> Gesendet: Freitag, 3. August 2007 18:00
> An: Valentin Zacharias
> Cc: Pat Hayes; John F. Sowa; [ontolog-forum]; Ivan Herman; Juan
> Sequeda; SW-forum list
> Betreff: Re: AW: [ontolog-forum] Current Semantic Web Layer Cake
> Wichtigkeit: Hoch
> >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/On
> tologyWorkshopSlides.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.
> >>
> >>
> >>  --
> >>  -------------------------------------------------------------------
> --
> >>  IHMC		(850)434 8903 or (650)494 3973   home
> >>  40 South Alcaniz St.	(850)202 4416   office
> >>  Pensacola			(850)202 4440   fax
> >>  FL 32502			(850)291 0667    cell
> >>  phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
> >>
> --
> ---------------------------------------------------------------------
> IHMC		(850)434 8903 or (650)494 3973   home
> 40 South Alcaniz St.	(850)202 4416   office
> Pensacola			(850)202 4440   fax
> FL 32502			(850)291 0667    cell
> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Saturday, 4 August 2007 18:45:01 UTC

This archive was generated by hypermail 2.4.0 : Thursday, 24 March 2022 20:41:05 UTC