Re: last-call comments on Namespaces in XML 1.1 of 5 September 2002

On Wed, 2002-11-13 at 10:51, C. M. Sperberg-McQueen wrote:
> 
> The following are personal comments on Namespaces in XML 1.1 from
> C. M. Sperberg-McQueen.  I apologize for being so late with them.
> They arise out of my work preparing draft comments for the XML Schema
> Working Group, but since it looks as if that WG may take a while to
> reach consensus on some issues, I send these now as is, as personal
> comments.

I got this message due to historical administrative arrangements,
but I'll take the sign from the gods as an opportunity to
endorse most of these comments, and to elaborate on one of them.


[...]
> I believe
> the outright false and misleading statements can be removed from the
> spec even without achieving consensus on the 'philosophy' of
> namespaces.

yes, let's.


[...]
> p3 editorial, SEVERE: The phrase "universal names", in conjunction
> with similar phrases (e.g. "universally unique" in p8) suggests to
> some readers names which are universally unambiguous.  Given a
> "universal name", such readers expect to be able to identify, without
> further information, a single object denoted by the universal name.
> 
> Since (in the view of some observers including me) the specification
> could, in fact, if written differently, have provided identifiers with
> such globally unique denotation, it will not be immediately obvious to
> all readers that the interpretation just given of the phrase
> 'universal names' is erroneous.  Since the spec does not, however, in
> fact provide globally unambiguous identifiers, it is unacceptable to
> describe it as if it did.

Hmm...

I agree that the namespace spec misleads folks into thinking
that it guarantees universally unique denotations.

While it doesn't provide that guarantee, I think
there's a network effect when users of the namespaces
spec (i.e. namespace designers) constrain themselves
to having unique denotations;
i.e. there's a cost to using the same qname to denote
different things.

This is a position I'm advocating in the TAG;
let's see... this point about ambiguity isn't
in our issues list per se, but it's discussed
in recent drafts
  http://www.w3.org/2001/tag/2002/webarch-20021112#pr-uri-ambiguity
and there's a related issue about URIs and QNames.
  http://www.w3.org/2001/tag/ilist#rdfmsQnameUriMapping-6


> The misleading description in paragraph 3 cost the XML Schema Working
> Group a substantial amount of time -- my estimate at the time was that
> it cost us six months, but it may have been more -- owing to
> misconceptions about the nature of the Namespace Recommendation caused
> more or less directly by this paragraph.  I believe this paragraph
> should be deleted and replaced by one which accurately describes what
> the specification does.  Possible replacement text:
> 
>      These considerations require that document constructs should have
>      names constructed so as to avoid name clashes between names
>      assigned by different designers, specifications, or naming
>      authorities.  This specification describes a mechanism, XML
>      namespaces, which accomplishes this.
> 
>      It should be noted that the namespace-qualified names described by
>      this specification are not guaranteed to have globally unique
>      denotations; because this specification does not constrain the
>      construction or internal structure of namespaces, it is possible
>      for the same qualified name to denote more than one object.

yes, possible; but it should be NOT RECOMMENDED
(in the sense of RFC2119) following

  http://www.w3.org/2001/tag/2002/webarch-20021112#pr-uri-ambiguity

I hope future TAG drafts motivate that principle better,
but I'm pretty confident it's an important one.

>  (For
>      example, in a namespace for a typical XML vocabulary, an element
>      type and a global attribute may have the same qualified name.)
>      Such names must be disambiguated by means not prescribed by this
>      specification; in practice, they are often disambiguated by
>      reference to the context in which they are used.
> 
> p4 s-2/-1 editorial: These last two sentences have proven more
> misleading than they seem to me to be worth.  They are in any case
> false, since (1) XML namespaces need not have any particular structure
> and (2) the namespaces used in conventional programm languages
> (e.g. the variable and function-name namespaces of Algol 60, C, Lisp,
> Pascal, etc.) are not sets.

quite.

[...]

> Appendix B The Internal Structure of XML Namespaces
> 
> This appendix may have seemed a good idea when Namespaces 1.0 was
> issued; it has not worn well, and has caused more confusion than it
> has avoided.  I believe it should either be rewritten or deleted.

yes, please.


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/

Received on Wednesday, 13 November 2002 13:42:51 UTC