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Re: What is truth anyways? was: Re: MISC: Internet Media Type registration: proposed TAG finding

From: patrick hayes <phayes@ai.uwf.edu>
Date: Wed, 12 Jun 2002 00:38:56 -0500
Message-Id: <p05111a02b92c8c25db8d@[65.217.30.94]>
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: "Dan Connolly" <connolly@w3.org>, www-rdf-logic@w3.org

>Gentlemen,
>
>I'm getting rather frustrated. Perhaps it is a mistake to write a model
>theory for RDF, as it appears too constraining.

What it constrains is what RDF inference engines are supposed to do. 
I WANT that to be constrained.

>Perhaps it actually would be
>better to let everyone interpret triples as they please -- I mean N3/CWM
>appears honestly useful, so why not allow
>http://www.w3.org/2000/10/swap/log#Truth to be a _Truth_ in the same sense
>that a truth defined by the RDF model theory is a truth (assertion) ?

The issue isn't the notion of truth. The issue is whether this 
notion, whatever it is, is part of the RDF spec or not. If it is, 
then RDF engines should be required to respect it. If it isn't, then 
I don't give a damn what it is, because its irrelevant to what an RDF 
engine does.

I agree that N3/CWM appears to be useful. If that were put forward as 
part of a spec for N3/CWM I would have much less to say about it. I 
mean, we could get technical, but at least we would be having a 
sensible discussion.  What Im objecting to is calling it "RDF".

BTW, if we are talking about people, then of course people can, and 
probably will, interpret triples as they please. So what? We can't 
legislate how people think.

>What
>is the harm in being so draconian in how we define truth?
>
>Isn't that how the internet works ... let a thousand flowers bloom ... and
>so why not allow a thousand truths?

OK, provided you agree that when the ATM talks to the bank and credit 
union computers, and those computers talk to the IRS computers, and 
they all use their own notions of truth, that you are happy with what 
happens to your bank account. And then of course there are the FBI 
computers and the NIMA computers....

Pat


>
>Jonathan
>
>
>>
>>  >On Wed, 2002-05-29 at 11:35, patrick hayes wrote:
>>  >[...]
>>  >>  >It wouldn't be unprecedented, by the way:
>>  >>  >
>>  >>  >   http://www.w3.org/2000/10/swap/log#Truth
>>  >>
>>  >>  Wow, scales fall from my eyes!
>>  >
>>  >Why is this so crazy? It doesn't seem interestingly
>>  >different from wtr in KIF.
>>
>>  The difference is fundamentally that the meaning of wtr in KIF is
>>  specified by a KIF model theory, not by English comments in a
>>  particular KIF document. So the KIF is (1) mathematically precise (2)
>>  part of the actual language specification (3) part of a semantics
>>  (and also, by the way (4) provably equivalent to a complete deductive
>>  system, although this isnt described in the KIF specs.)  None of that
>>  is true of the swap file.
>>
>>  >[...]
>>  >>  Seriously, that document (1) does not define logical truth in any way
>>  >>  whatsoever (2) says this: - <rdfs:Class
>>  >>  rdf:about="http://www.w3.org/2000/10/swap/log#Truth">
>>  >>     <rdfs:comment>Something which is true: belive it as you would
>>  >>  belive this. Understood natively by cwm in that it will execute rules
>>  >>  in a formula declared a Truth within a formula it is already taking
>>  >>  rules from.</rdfs:comment>
>>  >>
>>  >>  which seems to indicate that log#Truth in fact is simply supposed to
>>  >>  mean 'asserted', which is perfectly meaningful, but is not the same
>>  >>  as 'logically true'.
>>  >
>>  >Er... close to that; it's a de-quoting mechanism.
>>
>>  OK, that's fine. However, I note that this isn't specified in the RDF
>>  spec anywhere.
>>
>>  >  > And in fact, the document does not define *any*
>>  >>  meanings in RDF, or constrain the RDF interpretations, in any way
>>  >>  whatsoever. It is just English with RDF decorations added. (The CWM
>>  >>  code might be said to be a kind of implicit machine-readable
>>  >>  constraint on interpretations of this vocabulary - along the lines of
>>  >>  'this means whatever it takes to make CWM produce valid conclusions'
>>  >>  - but it goes well beyond what an RDF engine would be able to make
>>  >>  use of.)
>>  >
>>  >[...]
>>  >>  >>  Who discovers this, and how?
>  > >>  >
>>  >>  >As explained above, I (i.e. anybody using
>>  >>  >the framework) use the deployed URI infrastructure
>>  >>  >to dereference http://www.daml.org/2001/03/daml+oil#UniqueProperty
>>  >>  >and I see:
>>  >>  >
>>  >>  ><rdfs:Class rdf:ID="UniqueProperty">
>>  >>  >   <rdfs:label>UniqueProperty</rdfs:label>
>>  >>  >   <rdfs:comment>
>>  >>  >     compare with maxCardinality=1; e.g. integer successor:
>>  >>  >     if P is a UniqueProperty, then if P(x, y) and P(x, z) then y=z.
>>  >>  >     cf OIL FunctionalProperty.
>>  >>  >   </rdfs:comment>
>>  >>  >   <rdfs:subClassOf
>>  >>  >rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
>>  >>  ></rdfs:Class>
>>  >>  >
>>  >>  >The comment there is reasonably clear as a constraint
>>  >>  >on interpretations, no?
>>  >>
>>  >>  NO!!! It is not in any way a constraint on interpretations, any more
>>  >>  than a comment in a program is code.
>>  >
>>  >How is that not acceptable as a constraint on interpretations, but
>>  >stuff like this is?
>>  >
>>  >
>>  >[[
>>  >for ?D an XML Schema datatype, IO(?O) is the singleton set containing
>>  >the element of IC(?D) that has lexical representation ?L, provided that
>  > >there is one, otherwise IO(?O) = { }
>>  >]]
>>  >  -- http://www.w3.org/TR/2001/NOTE-daml+oil-model-20011218#3
>>
>>  The difference is that this stuff is in a description of the model
>>  theory, and is part of the language specification intended to be read
>>  by humans, not a comment attached to a piece of the formal language
>>  intended to be read by software. Nobody expects this to be readable
>>  by machines. But that earlier rdfs:comment isn't in a specification
>>  document intended for human readers, it's in a piece of formal RDF.
>>
>>  I agree with you that this particular rdfs:comment is so exact that
>>  it COULD be part of a semantic specification. Unfortunately, however,
>>  as a matter of fact it ISNT part of a semantic specification. It's
>>  labelled "comment",  and its not part of a published specification
>>  document, and it occurs inside some RDF, which is supposed to be
>>  machine-readable.  Comments, pretty much by their nature, are not
>>  parts of a formal semantic specification and are not supposed to be
>>  machine-readable.
>>
>>  >  > A comment is a COMMENT, and that
>>  >>  is all. YOU can read that and understand it, Dan, because you are a
>>  >>  HUMAN BEING WHO UNDERSTANDS ENGLISH. The whole point of the semantic
>>  >>  web is to allow SOFTWARE AGENTS to do a little understanding.
>>  >
>>  >Yes, so, I read the comment and write some code.
>>
>>  But we are talking about something that is supposed to be readable BY
>>  THE CODE, not by YOU. Thats why we are working on all these
>>  interminable specification documents, right? So that people can write
>>  code which will process the RDF unambiguously, and all their various
>>  pieces of code will do the right things with one another. RDF isn't
>>  meant for people to first read, then having read it, write code to
>>  interpret it. Its meant to be read by code that was already written
>>  by people who have never seen the particular RDF graph, but have read
>>  the RDF spec. Would you expect HTML to work if I had to re-write the
>>  code of my browser in order to read each web page?
>>
>>  >  > When
>>  >>  you can write a Perl script that can figure out the content of the
>>  >>  English comments, then maybe you can claim that the meaning of the
>>  >>  comments is part of the meaning of the formalism. It still wouldn't
>>  >>  be part of RDF, but you could call it RDFE .
>>  >
>>  >It seems to me to be a perfectly reasonable part of
>>  >the Resource Description Framework. I guess I'm willing
>>  >to call it an extension to RDF, if that makes you happy.
>>  >But it seems pretty arbitrary, to me.
>>
>>  It seems absolutely fundamental to me. Why are we even bothering to
>>  write a spec for RDF if one can include anything in it by writing
>>  arbitrary scripts?
>>
>>  >[...]
>>  >>  >Let's put it this way: does dublin core fit into the framework?
>>  >>  >Or is RDF+dc an extension? How about a document that
>>  >>  >uses RDFS, DAML+OIL, and dublin core together? Is that
>>  >>  >another sort of extension?
>>  >>
>>  >>  Dan, you cannot possibly be this obtuse. Surely you know the
>  > >>  distinction between a language and a set of axioms in that language.
>>  >>  DC is a set of assertions in RDF, right?
>>  >
>>  >No; it's a set of terms defined by a community of practice.
>>
>>  OK, then it isn't representable in RDF. You can't have it both ways.
>>  If RDF is warm and fuzzy and determined by human societal use, then
>>  it isn't processable by machines (until we have AI licked). If its
>>  processable by machines then all the formal meaning in it is
>>  determined by the machine-processable aspects of the spec: in the
>>  case of RDF, by RDF entailment of some kind. Of course humans might
>>  declare in some human-readable way (eg in a comment) that some RDF is
>>  *intended* by them to mean something, and maybe then they can be held
>>  to account for having published that and tried by a human jury and
>>  fined by a human judge and whatever. All true, and all totally
>>  irrelevant to the machine-processable aspects of RDF meaning. I could
>>  get prosecuted for writing libelous graffiti, but that doesn't make
>>  graffiti into RDF.
>>
>>  >There are semantics to the dublin core terms that aren't
>  > >written in the RDF specs.
>>
>>  Of course. But can they be represented in an RDF graph,  so that
>>  given the RDF graph and the RDF specs together you can figure out the
>>  semantics? If not, then claiming that there are such semantics, and
>>  simultaneously that the dublin core is 'in' RDF, seems to me to be
>>  close to dishonest. If RDF is a formalism, then RDF can only express
>>  RDF-expressible content.  And if RDF isn't a formalism, then why are
>>  we bothering to write all these formal specs that sure make it LOOK
>>  like a formalism? Are we trying to fool somebody, or what?
>>
>>  (Sorry if I sound like I feel strongly about this, but I do feel
>>  strongly. Ive been worrying and writing about what it means for a
>>  formal language to express meanings all my working life, and believe
>>  me, some pretty silly stuff has already been written; but at least in
>>  AI we now have a fairly clear overall picture of what it means to
>>  represent knowledge, including what it DOESNT mean. I joined the RDF
>>  effort in good faith to try to help make the SW happen. Now I feel
>>  like Ive been conned into signing a religious manifesto.)
>>
>>  >  > That means that one can
>>  >>  interpret those DC assertions using the RDF semantics and they mean
>>  >  > something that approximates to what the DC writers had in mind,
>>  >>  roughly. If you do that to DAML, you often *don't * get an
>>  >>  approximation of what the writer of the DAML had in mind.
>>  >
>>  >I must be quite obtuse; I don't see any fundamental
>>  >difference between partial understanding of DC semantics
>>  >and partial understanding of DAML semantics.
>>
>>  The difference is that you are here making a pun on 'semantics' .
>>  That word is used informally to just mean 'intended meaning' and
>>  formally to mean something like a model theory. Choose one sense and
>>  stick to it. In the second sense, DC doesn't even have a semantics.
>>  In the first sense, "DAML semantics" could be anything.
>>
>>  Basic AI/KR insight: if you formalize a thought or an idea, you can't
>>  just assume that what you had in mind is what is actually captured in
>>  the formalization. You have to examine the formalization carefully,
>>  poke it and shake it, to see what it really has in it.  Just writing
>>  "Loves(Pat, Jackie) " does not, by itself, capture that idea that I
>>  love somebody called Jackie. No amount of talking *in English* is
>>  going to change this. I can say it means that on my home page, write
>>  letters to the NY Times about it, put up billboards, stand on street
>>  corners and yell that that is what it means; none of that *makes* it
>>  mean that.  The only way to make a formal sentence mean something is
>>  to say enough *in the formalism* to constrain the interpretations *of
>>  the formalism* sufficiently, and/or to somehow ground the formalism
>>  to reality, e.g. by perceptual machinery.
>>
>>  Now, maybe English(/French/Kanji...) meanings could be used as a kind
>>  of social grounding, so that linking the formalism to NL sentences in
>>  a way that uses other people's experience as a kind of remote
>  > grounding is itself a social way of attaching meanings. So I can use
>>  the name 'Melbourne' with confidence even though I have never seen
>>  the place, never will, and have no idea what it looks, feels, sounds
>>  or smells like, because Im pretty sure that other people somewhere
>>  else have done enough seeing, feeling, listening and smelling to
>>  ensure that the name pins down a unique referent. That is what your
>>  vision of the 'greater RDF' sounds rather like. And that is indeed a
>>  great ambition; I mentioned it (briefly) in a paper I wrote in 1985.
>>  But we aren't going to achieve that by writing little essays inside
>>  rdfs:comments; we would need some genuine NL understanding software
>>  to be incorporated into the semantic web. Then (some of) NL will have
>>  been integrated into the formalism itself, and that *certainly* will
>>  not be RDF. Again, don't get me wrong: that's a fine long-term
>>  ambition to have for the SW. But please don't call it 'RDF', because
>>  that gives the impression that you are claiming that RDF 1.0, this
>>  useful but rather wimpy little language, can *already* incorporate NL
>  > meanings, human intentions, and arbitrary semantics; but in fact, it
>>  can't, no matter how much we put in the rdfs:comment strings.
>>
>>  Pat
>>  --
>>  ---------------------------------------------------------------------
>>  IHMC (850)434 8903   home
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>>  phayes@ai.uwf.edu
>>  http://www.coginst.uwf.edu/~phayes
>>
>>


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Received on Wednesday, 12 June 2002 01:39:02 GMT

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