Re: Boeing XRI Use Cases

We agree, or at least we appear to:  the empty string is legal as an IRI 
Reference and as a URI Reference.  The empty string is also a member of 
the value and lexical spaces of the XSD anyURI datatype.  The the empty 
string is also legal as the value of a namespace declaration in XML, that 
string is a distinguished value that is in fact used to cancel the 
corresponding prefix binding.  Accordingly, there are no namespaces named 
with the empty string.

> Relative and "empty string"  IRI are certainly valid IRI, the 
> question is if they are valid "anyURI" in XML 1.1?

I assume you mean XSD 1.1?  The specification says [1]:

"The ·lexical space· of anyURI is the set of possibly empty finite-length 
character sequences."  Earlier it says:

"[Definition:]   anyURI represents an Internationalized Resource 
Identifier Reference (IRI).  An anyURI value can be absolute or relative, 
and may have an optional fragment identifier (i.e., it may be an IRI 
Reference).  This type should be used when the value fulfills the role of 
an IRI, as defined in [RFC 3987] or its successor(s) in the IETF Standards 
Track. "

So, >any< sequence of characters, including the empty sequence, is a legal 
xsd:anyURI.  The specification says that anyURI >should< be applied when 
the string represents an IRI reference.  Conformance to IRI ref. syntax is 
thus strongly encouraged, but not enforced by the datatype.

> I discounted that as perhaps being non-normative given the 
> draft status and the other document.

If we're discussing XSD 1.1, then [1] is as authoritative a source as 
you'll find.  The only Recommendation-level version of XSD is 1.0 [2]. 
That version did try to enforce conformance to (pre-) IRI syntax, but 
clearly allows for relative and thus for empty forms.  I think there's 
very little question that XSD anyURI, whether 1.0 or 1.1,  allows for IRIs 
(perhaps modulo some edge cases in 1.0 as you say that you and DaveO 
uncovered some), allows for relative IRIs, and thus allows for the empty 
string.  We agree that the empty string is not and never has been usable 
as the name for an XML namespace.

Noah

[1] http://www.w3.org/TR/xmlschema11-2/#anyURI

[2] http://www.w3.org/TR/2004/PER-xmlschema-2-20040318/#anyURI



--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------








John Bradley <john.bradley@wingaa.com>
08/06/2008 12:32 PM
 
        To:     noah_mendelsohn@us.ibm.com
        cc:     "Booth, David (HP Software - Boston)" <dbooth@hp.com>, 
"Henry S. Thompson" <ht@inf.ed.ac.uk>, Julian Reschke 
<julian.reschke@gmx.de>, www-tag@w3.org
        Subject:        Re: Boeing XRI Use Cases


Hi Noah,

I don't claim to e an XML 1.1 expert.

I was looking at Sec 2.2 of xml-names11:
http://www.w3.org/TR/xml-names11/


> 2.2 Use of IRIs as Namespace Names
> The empty string, though it is a legal IRI reference, cannot be used 
> as a namespace name.
>
> The use of relative IRI references, including same-document 
> references, in namespace declarations is deprecated.
>
> Note:
>
> This deprecation of relative URI references was decided on by a W3C 
> XML Plenary Ballot [Relative URI deprecation]. It also declares that 
> "later specifications such as DOM, XPath, etc. will define no 
> interpretation for them".
>

I should have used "empty string" rather than null.

There seems to be a conflict between the two documents.

The reference to relative IRI XML schema re 3.3.18 of xmlschema11-2 is 
in a [Definition:]

I discounted that as perhaps being non-normative given the draft 
status and the other document.

Relative and "empty string"  IRI are certainly valid IRI, the question 
is if they are valid "anyURI" in XML 1.1?

It is worth someone having a look at, but probably someone closer to 
it than me.

However I don't think it is particularly relevant to XRI though I 
suppose  that relative XRI would also be prohibited according to xml- 
names1.1.   I don't think I am going to lose sleep over that:)

The XRI specs don't rely on any new functionality in XML 1.1.

Regards
John Bradley
OASIS IDTRUST-SC
http://xri.net/=jbradley

五里霧中




On 6-Aug-08, at 7:29 AM, noah_mendelsohn@us.ibm.com wrote:

> John Bradley writes:
>
>> The definition of "anyURI" changes slightly to include the
>> mapping of http: IRI according to RFC3987 This allows for the
>> ireg-name component to be mapped via RFC3490 for schemes using
>> domain names.
>
> OK, good.
>
>> In XML schema 1.1 that is almost done [http://www.w3.

>> org/TR/xmlschema11-2/]
>
>> [...] allows almost all http: scheme IRI to work as "anyURI",
>> relative and null IRI are excluded so it is still a sub set,
>> though a much larger one than before.
>
> Hmm, I don't see where relative or "null" are excluded.   The
> specification for that datatype says [1]:
>
> "[Definition:]   anyURI represents an Internationalized Resource
> Identifier Reference (IRI).  An anyURI value can be absolute >>or
> relative<<, and may have an optional fragment identifier (i.e., it 
> may be
> an IRI Reference)."
>
> Was there something else you meant when you said that "relative [is]
> excluded"?  I read this as explicitly allowing relative.  As to "null"
> IRIs, the word null does not appear in RFC 3987 [1] or in RFC 3986 
> [2] for
> that matter, but RFC 3987 includes the following grammar:
>
>   IRI-reference  = IRI / irelative-ref
>
>   irelative-ref  = irelative-part [ "?" iquery ] [ "#" ifragment ]
>
>   irelative-part = "//" iauthority ipath-abempty
>                       / ipath-absolute
>                       / ipath-noscheme
>                       / ipath-empty
>
>   ipath-empty    = 0<ipchar>
>
> This seems to me to indicate that an IRI Reference, as required by XML
> Schema 1.1, can indeed be an ipath-empty, I.e. the null string.  Am I
> still missing something?
>
> Noah
>
> [1] http://www.ietf.org/rfc/rfc3987.txt

> [2] http://www.ietf.org/rfc/rfc3986.txt

>
> --------------------------------------
> Noah Mendelsohn
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
>
>
>
>

Received on Wednesday, 6 August 2008 17:28:12 UTC