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Re: review of LCC documents as of 26 December 2002

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Tue, 14 Jan 2003 19:33:43 +0000
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
cc: www-rdf-comments@w3.org
Message-ID: <28022.1042572823@hoth.ilrt.bris.ac.uk>

>>>"Peter F. Patel-Schneider" said:
> Dave said: 
>> This section has useful examples that are correct rdf/xml as well as
>> explaining the ideas that the grammar uses such as node element,
>> property element, etc.  If there are specific things 6 & 7 are silent
>> on that you need clarifying, please list them.
>
> The point is that I don't know whether there are any missing pieces of
> Sections 6 and 7, nor does, I suspect, anyone else.  (There may be a
> general consensus that Sections 6 and 7 are exhaustive, but no certainty as
> of yet.)  The way the document is now structured, however, means that if
> there are any such missing pieces, and if some example is not covered by
> Sections 6 and 7, then this example extends the treatment given in Sections
> 6 and 7.

At this date, I have seen several implementations of the RDF/XML
syntax from this grammar which pass all the RDF Core parser test
cases.  So I would say that, given this evidence, the general
consensus is that it is complete.

> In general, examples should only be illustrative, and never normative.
> First, there are just too many things that can go wrong in an example.
> Second, there is no way to cover a non-finite category with examples.

Many (most, I would say) W3C Recommendations have normative examples
and that seems to be good practice.

This document benefits from such examples that are more than just
informative, they are correct or "of the norms", which is what
normative means.  They have been found useful in explaining the
syntax as well as illustrating the terms used in defining the syntax
such as Node Element.

<snip/> 
> > > Section 5: 
> > > 
> > > What does it mean for a namespace to contain a set of names?  How is this
> > > regulated in RDF?  Can the owner of any namespace close off the namespace
    ?
> > > How can this be done in RDF?  Without answers to these questions, saying
> > > that the RDF namespace contains only a certain set of names doesn't make
> > > sense.
> > 
> >   [Definition:] An XML namespace is a collection of names, identified
> >   by a URI reference [RFC2396]
> > 
> >   -- http://www.w3.org/TR/1999/REC-xml-names-19990114/
> > 
> > The RDF namespace given here is just such an XML Namespace - a
> > collection of names identified by a URI reference.  Section 5.1 tells
> > you what the names are by listing them along with a rule for the
> > constructed ones of the _n form and gives you the URI reference.
> > 
> > The other questions are best directed at what XML namespaces are
> > about since the RDF model does not have a concept of namespaces.
> 
> If the notion in Section 5.1 is an XML Namespace, then it should correspond
> to that notion.  The XML Namespace document is quite vague as to the
> contents of a namespace, but I don't see in it anywhere the notion of being
> able to enumerate the names in a namespace, nor removing a name from a
> namespace.  

I think we defined (the collection of names, the URI reference) in
the RDF namespace clear enough.  Your issues here are more to do with
the clarity of the XML Namespaces specification than this document.

Other specifications do something very similar.  Picking one at
random, the SVG 1.1 Recommendation (out today) gives the namespace
URI in a section http://www.w3.org/TR/SVG11/intro.html#Namespace and
the names in a DTD and a list of elements.

The collection of names in the RDF namespace changed, which is why
the note is there.


> > > The container property names are not of the form _n where n is a positive
> > > integer, they are of the form _n where n is a  base-10 numeral without
> > > leading zeros that represents a positive integer. 
> > 
> > Not just positive; 0 is forbidden.  How about
> >   "where n is a decimal integer greater than zero with no leading zeros"
> 
> Well, 0 is generally not considered to be a positive number, just a
> non-negative number, but if you think that ``greater than zero'' is better
> than ``positive'' go ahead and use that.

In a previous draft we had "non-negative" which was both worse and
wrong since it didn't exclude 0.  I asked a few people informally and
some thought positive included 0 so changing to use greater than zero
seems better.

I will change it to be like:
  "where n is a decimal integer greater than zero with no leading zeros"


> > > Section 8: 
> Well, the very first sentence of Section 8 says that
> 
> 	There are some RDF Graphs as defined in the RDF Concepts and
> 	Abstract Syntax Working Draft that cannot be serialized in RDF/XML.
> 
> Either this or
> 
> 	... now allows all graphs with blank nodes to be serialized.
> 
> must be wrong, I believe that the former sentence is correct and the latter
> phrase is incorrect.

No, both are correct.

Here is an example of a legal RDF graph written in N-Triples that
cannot be serialized into RDF/XML: 

<http://example.org/foo/> <http://example.org/bar/> <http://example.org/blah/> .

Though it has no blank nodes, the predicate URI
http://example.org/bar/ cannot be written as an XML QName.  This is
is already explicitly listed as the first condition in section 8:

  [[Use property names that cannot be turned into XML
    namespace-qualified names.]]

(It has been suggested that you can serialize it when you have a
schema-aware system, since you could use a subProperty of
relationship to a predicate that could be serialized)

Dave
Received on Tuesday, 14 January 2003 14:36:29 GMT

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