W3C home > Mailing lists > Public > www-archive@w3.org > June 2003

irc log re rdf:first, Social Meaning, URI dereferencing

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 25 Jun 2003 11:47:47 -0400
Message-Id: <200306251547.h5PFllLb024880@roke.hawke.org>
To: www-archive@w3.org


[This is a transcript of an IRC conversation on a W3C internal
channel, which we decided really ought to be public.]

<sandro> Hrm.   There's text in RDF Semantics talking about
rdf:first/etc which is absolutely incompatible with
semantics-are-defined-by-URI, I think.     What to do about that......

<tim-cape_> incompatible?

<sandro> yeah.       "RDF Semantics" says for instance that   { _:x
rdf:first _:y, _:z } does NOT entail that _:y and _:z denote the same
thing.  Fine.  We knew that.   But then it says that "Semantic
extensions MAY" do this.     That is, using the *same* URIs, and RDF
graph would mean two different things, depending on which "semantic
extensions" (like RDFS and OWL) were being used.

<sandro> Thus RDF graphs need to be transmitted in an envelope which
says which semantic extensions are being committed to. 

<sandro> (and which ontologies are being committed to, meanwhile)

<sandro> ... and dereferencing the URI is not enough.

<sandro> I'm not saying we have to change the specs or stop RDF Core,
but I think we really need to be honest about where RDF fits into the
semantic web.   And the answer, increasingly, is that you can't just
transmit RDF.   You need private agreements about it, etc. 

<tim-cape_> no no no no no

<danbri> how do you feel about that, tim?

<tim-cape_> the whole point about it is atht eth web protocols ARE
private (rather public really) agreements. 

<danbri> the old M+S RDF spec didn't assert the transistitv of
rdfs:subClassOf, but didn't outright dispute it, so RDFS could come
along and claim it was transitive (in prose); and OWL could say that
for machines. When we say that RDFCore's semantics don't (thmselves)
claimg rdf:first to be functional (or whatever) I hope it is in the
same vein, ie. they leave the window open for later claims. 

<danbri> feel free to copy that to #rdfig if context arises where it
would make sense 

<DanC> not private agreements; the ontologies are public; the envelope
is the web. 

<sandro> I'm having trouble understanding what Tim means by "the whole
point about it is atht eth web protocols ARE private (rather public
really) agreements." 

<sandro> I'd say: the whole point is that the web protocols are public
agreements, also known as "standards". 

<danbri> are individual ontologies 'standards'?

<sandro> Yes.    Microstandards.  :-)

<DanC> tim's just saying that where sandro said "RDF relies on private
agreements" timbl agreed, and said that web protocols serve as
"private agreements" though they're actually quite widely
disseminated, for the most part 

<DanC> individual ontologies can also form part of the agreement,
though we don't expect everybody to be party to them; only those that
have read them; e.g. those that use URIs from them. 

<sandro> Hrm.  My point is that there's a gap between web protocols
and RDF, where no one gets to say which extensions & ontologies they
are using with their RDF. 

<DanC> I think the "follow your nose" principle fills the gap. 

<DanC> i.e. if you use ont:term, you're party to ont

<sandro> Right, but Pat's prose in "RDF Semantics" actively refutes
that, saying that RDF semantic extensions may define rdf:first
differently. 

<sandro> s/may/MAY/

<DanC> not inconsistently; they can further refine it

<DanC> just like rdf:type is further refined by the definition of
every class

<DanC> formally, in the general case, any ontology can restrict the
satisfying interpretations arbitrarily. 

<TimB-L> Sandro, people should not be disputing what rdf:first means -
they should be disputing simply which set of inference axioms they are
going to expect of a given operation, quesry etc. 

* sandro considers Dan's argument....

<DanC> s/not inconsistently/not non-monotonically/

<TimB-L> I ahve just printed off http://www.w3.org/TR/rdf-mt/

<sandro> I don't see the difference there, Tim.      Can a collection
have more than one first element?     Doesn't the answer to that
affect what   {x rdf:first y, z} means? 

<DanC> er... that dates from Feb, no tim?

<TimB-L> You are saying that the problem only exists in a later
version and you can't get ca consensus on #rdfig about which version
it is. 

* DanC isn't sure what problem tim is looking for

<DanC> oh.. the first/rest thing... dunno if that's changed much
lately 

<sandro> I'm saying the problem exists in that version -- I haven't
looked at the later version, but I thought I/we should.    

<TimB-L> me l;ooking for problem: Sandro:  Hrm. There's text in RDF
Semantics talking about rdf:first/etc which is absolutely incompatible
with semantics-are-defined-by-URI, I think. What to do about
that...... 

<sandro> But DanC has a different angle, I suppose.   That Pat's
saying while rdf:first means one thing, people are free to
additionally constrain it. 

<TimB-L> No, not nayone is free to additionally constrain it. 

<danbri> but not contradict it...

<TimB-L> But the owners can explain more stuff about itas they find
out how.

<danbri> <sandro> yeah.       "RDF Semantics" says for instance that
{ _:x rdf:first _:y, _:z } does NOT entail that _:y and _:z denote the
same thing.  

<DanC> I thought we agreed that OWL could further constrain
rdfs:range, timbl

<danbri> 'does NOT entail' is different to 'doesn't say that it
entails' 

<danbri> isn't it? 

<TimB-L> Might not be.

<TimB-L> entail under _______

<danbri> yup, rdfc-entail...

<TimB-L> "entail under the axioms gioven in this document"

<TimB-L> So there are different sets of axioms one can use, all
subsets of some imaginary set of all true axioms written in some
imaginary suitablly expressing language.

<sandro> (Pat actually does use the words "does not entail" for that
example.    6th paragraph of
http://www.w3.org/2001/sw/RDFCore/TR/WD-rdf-mt-20030117/#collections
Of course he means "doest not [RDF simple] entail" 

<TimB-L> He ios talking about the existence of lists there

<TimB-L> he has <ex:aaa>   which may not be what he means. Weird URL.

<TimB-L> I think he means ex:aaa

<DanC> it's a wierd URL alright, but I asked, and he really does mean
<ex:aaa> 

<TimB-L> { ( ex:aaa ex:bbb ) }   => {  ( ex:bbb ex:aaa ) }. 

<TimB-L> We should him to stop encouraging people to invent new URI
schemes. 

<sandro> axioms are kind of a middle ground between formal semantics
and running code.    "RDF Semantics" says there is "RDF simple
entailment" and then there are extensions.     The rdf:first example
entailment I gave is a non-entailment under "rdf simple entailment"
and also under RDFS entailment.    But Pat says you're free to make
extensions.     I thought we wanted to indicate which extensions were
being used by the presence of URIs, but that wont  work in this case,
since it's still rdf:first. 

<TimB-L> but anyway.

<TimB-L> Should I send in in a comment on that document?

<sandro> It's too late for that, as I understand it.

<sandro> As I understand it, unless there is outstanding dissent from
before-deadline comments or within the WG, there's nothing anyone can
do to stop this from going through to Rec. 

<sandro> or the WG can re-open the issue in the face of new evidence. 

<TimB-L> We can annotate the rdf schema with a pointer to others 

<TimB-L> Like a pointer to a rules! 

<TimB-L> Like a pointer to rules! 

<sandro> I can't figure out whether the WG missed important evidence
here about how extensions/ontologies were supposed to work, or
not.... 

<TimB-L> {    ?x rdf:rest ?y } =>   {  ?y a rdf:List }.

<TimB-L> Or whether they got lost in the rest of the document.

<TimB-L> The semantics in the document are very weak ly written.
"intended to be used ...' 

<sandro> The question here, I think, is who can say:   { ?x rdf:first
?y, ?z } => { ?y owl:sameAs ?z }            aka     rdf:first a
owl:FunctionalProperty.  

<danbri> anyone. but who would be believed? 

* danbri looks forward to digitally-signed W3C specs 

<sandro> danbri, if you said that, would I know you were lying?
rdf:first is NOT defined by the W3C specs to be an
owl:FunctionalProperty. 

<danbri> yet 

<sandro> in rdf 3.0? 

<danbri> could be. 

<sandro> that would be an incompatible change, of course. 

<danbri> that would be consistent with the way things have evolved

<danbri> we have model of 'same thing, more claims about it'

<sandro> But the more claims about it may render someone else a liar.
That's not fair. 

<sandro> esp when we told them they were free to make more claims
about about it themselves. 

<danbri> I'm happy to deploy on top of RDF. A liar or a partial
truth-teller. Since the earlier claims weren't expressed in a
machine-way, nor was their implicit scoping, so it's all out of
machine's reach anyway. 

<TimB-L> I think the question would be, who owns the URI?

<TimB-L> And w3.org owns it and so we can settle it.

<TimB-L> We have a process.

<TimB-L> One working group can in fact continuet the work of another.

* DanC encourages technical discussion to move to #rdfig or some other
  googleable space

<sandro> And our LC draft settles it.  It says user "may" use
rdf:first in all sort of other ways.

* TimB-L wishes we could stream the tape of this one onto #rdfif
  without a big mess

<DanC> mailing it to www-archive makes it googleabel

* sandro would be happy with having this logged and permitting
  sections of the log.

<sandro> yeah

* DanC prepares for rdf calendar chat...

<danbri> anything i've said today here, am happy -> google

* TimB-L would be happy with this being public, esp cleaned up.

<danbri> hmm anybody/somebody/nobody'll do it... 

<TimB-L> W3C owns the IRI.  The OWl working group is
refining/extending  the work of the RDF Core group.

<TimB-L> s/IRI/URI

<sandro> I'd rather run the problem into the ground before google even
gets around to it, myself.

<sandro> but I understand the concern that that wont happen.

<sandro> So the W3C is free to change rdf:first into being a
FunctionalProperty at some point in the future, even though that may
break applications written by someone adhering to our specs?

<TimB-L> rdf:first I belive is a functional property.  That is what
the group intended and what people expect.  Just that RDF core was not
in a position to say so  because they didn't know how to specify
conformnace to a small set of expected entailments wseparately from
the intended full meaning of the term.
Received on Wednesday, 25 June 2003 11:55:06 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 7 November 2012 14:17:31 GMT