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Re: ISSUE-83 (CURIEs must require colon): CURIEs are dangerous when used in combination with @vocab and @about [LC Comment - RDFa Core 1.1]

From: Shane McCarron <shane@aptest.com>
Date: Sun, 06 Feb 2011 10:34:35 -0600
Message-ID: <4D4ECD9B.30606@aptest.com>
To: nathan@webr3.org
CC: RDFa Working Group WG <public-rdfa-wg@w3.org>, Manu Sporny <msporny@digitalbazaar.com>
I appreciate what you are trying to do here, but I don't then understand 
what you propose to do with @vocab?  In your original mail about this 
issue you mentioned:

> <div vocab="http://xmlns.com/foaf/0.1/" about="#me">
>     My name is <span property="name">John Doe</span> and ..
> </div> 

about would still take the datatype SafeCURIEorCURIEorURI.  I think what 
you are proposing means that "#me" is not a legal CURIE, so this becomes 
a relative URI reference to the current base.  Which is of course what 
was intended in the fragment above.  Unfortunately, this change would (I 
think) destroy the main use case for @vocab - referencing CURIES in all 
situations without a prefix.  Now, I agree that there seem to be 
problems with that use case anyway, but I want us to make this change 
with our eyes all the way open.  If a CURIE cannot take the form 'curie' 
any longer, we are making a MAJOR change to the definition of a CURIE.  
I don't think this change is incompatible with the use cases in the Role 
Attribute specification, but it might be incompatible with other CURIE 
consumers out there.  And that would be bad.

Also, I would point out that this is a backward compatibility change.  
RDFa Syntax 1.0 explicitly permits the use of a CURIE with no prefix and 
no colon, although the RDFa specification itself does not use this feature.

If there is a way to fix this problem in RDFa without breaking faith 
with the original CURIE definition, I would prefer that.  We could, for 
example, continue to say there is no 'no prefix' mapping in RDFa.  
Actually, I think we can do this and everything will be fine.  We 
specified the 'no prefix' mapping via @vocab, but there is really no 
need to do that.  The text in section 7.4.3 clearly describes @vocab as 
something that effects interpretation of 'TERM's - so it has nothing to 
do with CURIEs.

Anyway, that would be my preferred way of dealing with this so we don't 
have a compatibility problem with anyone who might be counting on RDFa 
supplying the canonical definition of what a CURIE is.



On 2/5/2011 6:02 PM, Nathan wrote:
> RDFa Working Group Issue Tracker wrote:
>> ISSUE-83 (CURIEs must require colon): CURIEs are dangerous when used 
>> in combination with @vocab and @about [LC Comment - RDFa Core 1.1]
>>
>> http://www.w3.org/2010/02/rdfa/track/issues/83
>
> Note, this also affects @resource - there's more on the issue here:
>
>  http://lists.w3.org/Archives/Public/public-rdfa-wg/2011Feb/0032.html
>
> I've went through some different approaches and the one thing that 
> appears to clear up both this issue, and the others mentioned, is to 
> change the definition of CURIE so that the ':' is always present.
>
> Here's some proposed text for the CURIE syntax section:
>
> [[
> The key component of RDF is the URI, but these are usually long and 
> unwieldy. RDFa therefore supports a mechanism by which URIs can be 
> abbreviated, called 'compact URIs' or simply, CURIEs.
>
> A CURIE is comprised of two components, a prefix and a reference. The 
> prefix comprises an optional prefix_name and always ends with a single 
> colon (:).
>
> The general syntax of a CURIE can be summarized as follows:
>
>   prefix_name  ::=   NCName
>   prefix       ::=   [ prefix_name ] ':'
>   reference    ::=   irelative-ref (as defined in [RFC3987])
>   curie        ::=   prefix reference
>   safe_curie   ::=   '[' prefix reference ']'
>
> Note: The prefix_name consisting of the single char '_' is reserved 
> for usage with BlankNodes and has special meaning, implementations 
> MUST NOT allow this prefix to be associated with a URI.
>
> In normal evaluation of CURIEs the following context information would 
> need to be provided:
>
> - a set of mappings from prefixes to URIs;
> - a mapping to use with the default prefix (for example, :p);
> - a mapping to use with the '_' prefix, which is used to generate 
> unique identifiers (for example, _:p).
>
> In RDFa these values are defined as follows:
>
> - the set of mappings from prefixes to URIs is provided by the current 
> in-scope prefix declarations of the current element during parsing;
> the mapping to use with the default prefix is the current default 
> prefix mapping;
>
> - the mapping to use with the '_' prefix, is not explicitly stated, 
> but since it is used to generate bnodes, its implementation needs to 
> be compatible with the RDF definition and rules in Referencing Blank 
> Nodes. A document should not define a mapping for the '_' prefix. A 
> Conforming RDFa Processor must ignore any definition of a mapping for 
> the '_' prefix.
>
> If there is no in-scope mapping for a prefix, then the value is not a 
> CURIE.
>
> Note that the resulting URI must be a syntactically valid IRI 
> [RFC3987]. For a more detailed explanation see CURIE and URI 
> Processing. Also note that while the lexical space of a CURIE is as 
> defined in curie above, the value space is the set of IRIs.
>
> ]]
>
> This ensures all prefixes include the ':', removes the "no prefix" 
> mapping (which @vocab set), ensures that prefixes are defined in the 
> same way as the other specs, and also means that CURIEs and Terms are 
> now unambiguous, such that:
>
>   ':' valid CURIE
>   ':me' valid CURIE
>   'foaf:me' valid CURIE
>   'name' valid Term.
>
> Note that some other minor text changes may need to be made to the 
> draft if this were accepted, and that the definition of @prefix would 
> need to change to:
>
>  prefix
>   a white space separated list of prefix-name URI pairs of the form
>   prefix ' '+ xs:anyURI
>
> Which would also allow people to then do:
>
>   prefix=": http://example.org/foo#"
>
> (which they can't currently)
>
> Best,
>
> Nathan

-- 
Shane P. McCarron                          Phone: +1 763 786-8160 x120
Managing Director                            Fax: +1 763 786-8180
ApTest Minnesota                            Inet: shane@aptest.com
Received on Sunday, 6 February 2011 16:35:21 UTC

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