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Re: review of LCC documents as of 26 December 2002

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Thu, 02 Jan 2003 13:53:34 +0000
Message-Id: <5.1.0.14.0.20030102132056.0409b478@0-mail-1.hpl.hp.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: www-rdf-comments@w3.org

At 12:48 31/12/2002 -0500, Peter F. Patel-Schneider wrote:

[...]

>I think that the best solution to this problem would be to identify and
>move *all* the normative information into either the Syntax document or the
>Semantics document and then label the Primer, Concepts, Schema, and Tests
>documents as informative.

Thank you for the suggestion.


> > >RDF Schema is not described in terms of RDF.  This error, which has been
> > >made in several other places, must be ruthlessly eradicated.  Instead, RDF
> > >Schema is a semantic extension to RDF.
> >
> > Hmm, I'm not sure that the intended audience for this document will
> > appreciate the difference.  Whilst I don't want to say anything that is
> > technically incorrect,  this document also needs to avoid over reliance on
> > understanding model theory.  I've modified the passage in question to:
> >
> > [[
> > RDF's vocabulary description language, RDF Schema, is an extension of
> > RDF.  All RDF vocabularies share some basic common structure: they 
> describe
> > classes of resource and types of relationships between resources. RDF
> > Schema uses RDF graphs to describe these classes of resources and
> > relationships.
> > ]]
>
>This is still unacceptable to me.  The RDF documents need some way of
>distinguishing semantic extensions (like RDFS) from things that fit within
>RDF or RDFS (like the formal part of the Dublin Core).  RDF Core needs to
>make this distinction perfectly clear to readers.

Perfection is something we strive for, yet rarely achieve.

My current understanding of your objection is:

  o that the new text does not say anything that is false
  o the new text does not state something you consider it important to make 
clear
  o that which you desire be made clear is a technical issue for semanticians
  o that which you desire made clear is made clear in the semantics doc

If that understanding is correct, I see no problem, so I presume my 
understanding is incorrect.  Please help me understand.


> > >This document again makes the claim that RDF ``allows anyone to extend the
> > >description of existing resources, one of the architectural principles of
> > >the Web''.  Again, would that this were so.  There are many statements in
> > >the RDF documents and being currently made in the RDF Core WG that
> > >contradict this claim.
> >
> > Just as it takes two to tango, it takes at least two to contradict.  Can
> > you help me out here with a more specific objection.
>
>The discussion concerning allowing ``owners'' of resources to control their
>use runs counter to this claim.

What discussion?  This is what URL's are for.

>   Also the Concept document says that
>``[c]ertain URIs are reserved for use by RDF, and may not be used for any
>purpose not sanctioned by the RDF specifications''.

I don't see a contradiction there.


>[..]
>
> > >Section 2:
> > >
> > >Property is a technical term in RDF and should not be used for other
> > >purposes.
> >
> > I'm not sure what text you are objecting to here.
>
>``Only one of these classes has the property that it was defined by the tax
>office, ....''

Right,  and the term 'property' is correctly used in the technical sense to 
which you refer.


> > >What is ``common set theory''?  It would be much better to be more precise
> > >here.
> >
> > The witless response to that is "how much better, precisely" :)
> >
> > Again, I could have said "standard (Zermelo-Fraenkel) set theory", as in
> > the MT.  But I was wary of the word standard and I don't expect
> > "Zermelo-Fraenkel" to mean much to much of the audience of this
> > document.  I'm inclined to stick with things as they are, unless of course
> > I get further comment that there is a real benefit to the audience of this
> > document in being more precise.
>
>Well common set theory is an undefined term.  You are allowing sets that
>contain sets so you are going outside of flat sets.  As long as you have
>gone that far, why not just say ``Zermelo-Fraenkel set theory''?  Any reader
>that understands sets enough to understand the problem should not be
>troubled by this reference.

I agree it doesn't do any harm to mention it in passing.  Fixed.


>The general problem here is that a little description is a dangerous
>thing.  It is better to either ignore the issue or to be reasonably precise
>and comprehensive.
>
>[...]
>
> > [[The RDF specifications define the following classes.]]
> >
> > >  The Concepts document claims otherwise.
> > >What does it mean that the core RDF specifications define a class?  What
> > >does it mean for a thing to be described by RDF?
> >
> > I really have no idea what you are getting at here.  Is there some more
> > specific way you can make this comment?
>
>Concepts states that
>         Vocabulary terms in the rdf: namespace are defined in section 5.1
>         of the RDF syntax specification.
>but you include several terms form the rdf: namespace in your list.

Hmm, I think the intent is that 5.1 lists the names in the rdf namespace 
but does not define their meaning.

I think this is a comment on the concepts doc rather than schema.


> > >Section 3:
> > >
> > >The RDF semantic does not support the inference that properties with no
> > >rdfs:range or no rdfs:domain have a range or domain of rdfs:Resource.  In
> > >any case, this would be a non-monotonic inference as stated.
> >
> > Are you referring to, in 3.1
> >
> > [[In this specification, where no rdfs:range is specified for a property,
> > the rdfs:range of that property is rdfs:Resource.]]
> >
> > and in 3.2
> >
> > [[In this specification, where no rdfs:domain is specified for a property,
> > the rdfs:domain of that property is rdfs:Resource.]]
> >
> > This was an editorial judgement.  The intent here is that, in the 
> interests
> > of brevity, the text omitted statements that the domain and range of
> > properties were rdf:Resource.  The summary table however, and the rdf/xml
> > representation of the schema has these in full.
> >
> > No inference is stated or implied.
>
>How can you say this?  If no rdfs:domain is specified for a property, then
>there is *no* rdfs:domain for that property.  To say otherwise is just
>incorrect!

Its all to do with layering.

> >
> > However, if this is not clear, it would be possible, though tedious, to go
> > back and add in the text.
> > Are you sure this is necessary?
>
>Yes, YES ***YES***!

OK.

[...]

> > >It is more than misleading to say that RDF Schema does not specify how
> > >domains and ranges are to be used.  The RDF semantic states precisely how
> > >domains and ranges are to be used.
> >
> > Oh?  Where exactly?  We have tried to be careful to stay away from any 
> sort
> > of processing model.  I grant you that RDF Semantics specifies what
> > entailments are justified, but that is not the same thing as how they 
> might
> > be used.
>
>The RDF semantics states that domains and ranges are used to eliminate
>certain interpretations what might otherwise be valid.  (The use of a
>notion is not tied to a processing model.)

The current text says:

   [[but does not say whether or how an application should use it.]]

The applicable concept here is not "use", but "application use".  Whilst to 
you, an applications using a vocabulary for data validation, for inference 
and for constructing a useful user interface might all be doing the same 
thing, i.e. "restricting the set of interpretations", I don't agree that 
language is helpful in making the point we are trying to make.

I believe the meaning of the text will be clear to its intended audience, 
an opinion I am willing to revise in the light of other feedback to the 
contrary.


>[...]
>
> > >  and these other things may
> > >even be reasonable extensions of RDF, but any allusion to such activities
> > >needs to have a very strong disclaimer attached to it.
> >
> > This section is present to deal with a common issue raised about RDF.  The
> > term 'schema' tends to be associated with validation and this has led to
> > much confusion. All this section is saying that domain and range may be
> > used in different ways by different applications.  It is important to 
> say that.
>
>It is important *not* to say that in a place or manner that might cause it
>to be construed as part of the definition of RDFS.  Because this document
>has some sort of normative status, great care should be taken not to put
>more into RDFS than is actually there.

Would marking the section as informative rather than normative help?

[...]

Brian
Received on Thursday, 2 January 2003 08:52:47 GMT

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