Re: ISSUE-69 (xml and xmlns prefixes): Should the xml and xmlns prefixes be pre-defined in the default profile? [LC Comment - RDFa Core 1.1]

Just for our own record, here is what the namespace spec says

[[[
The prefix xml is by definition bound to the namespace name http://www.w3.org/XML/1998/namespace. It MAY, but need not, be declared, and MUST NOT be bound to any other namespace name. Other prefixes MUST NOT be bound to this namespace name, and it MUST NOT be declared as the default namespace.

The prefix xmlns is used only to declare namespace bindings and is by definition bound to the namespace name http://www.w3.org/2000/xmlns/. It MUST NOT be declared . Other prefixesMUST NOT be bound to this namespace name, and it MUST NOT be declared as the default namespace. Element names MUST NOT have the prefix xmlns.

All other prefixes beginning with the three-letter sequence x, m, l, in any case combination, are reserved. This means that:

	• users SHOULD NOT use them except as defined by later specifications

	• processors MUST NOT treat them as fatal errors.

Though they are not themselves reserved, it is inadvisable to use prefixed names whose LocalPart begins with the letters x, m, l, in any case combination, as these names would be reserved if used without a prefix.
]]] http://www.w3.org/TR/REC-xml-names/

The problem is that if we follow this, then the additional constraint "...MUST NOT be bound to any other namespace name" should also be followed, and we have no mechanism for such restrictions in RDFa Core. Also, if we follow the restrictions, we should also enforce the restriction on the xmlbla prefix which, according to the document, is not to be used.

Ie, the only thing we can do, without adding additional mechanisms to our prefix management, is to reinforce a default definition for xml and xmlns. Which is fine, but we should know about this.

That being said: we do have a mechanism for default profile that we define for XHTML. But we do _not_ have that for RDFa Core at the moment. Does it mean that we would have, conceptually, a default profile for Core? It is a possibility, and we could use the core default profile to add some well-known prefixes, a discussion we are having elsewhere...

Cheers

Ivan



On Jan 1, 2011, at 22:04 , RDFa Working Group Issue Tracker wrote:

> 
> ISSUE-69 (xml and xmlns prefixes): Should the xml and xmlns prefixes be pre-defined in the default profile? [LC Comment - RDFa Core 1.1]
> 
> http://www.w3.org/2010/02/rdfa/track/issues/69
> 
> Raised by: Manu Sporny
> On product: LC Comment - RDFa Core 1.1
> 
> As discussed by Toby and Gregg in the following thread (bottom of the response e-mail):
> 
> http://lists.w3.org/Archives/Public/public-rdfa-wg/2010Dec/0076.html
> 
> The RDFa WG should decide whether or not to declare the xml and xmlns prefixes in the default profile.
> 
> 
> 


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf