[whatwg] Alternative method of declaring prefixes in RDFa (was Re: RDFa is to structured data, like canvas is to bitmap and SVG is to vector)

[Henri Sivonen]

On Jan 19, 2009, at 02:18, Manu Sporny wrote:

> Toby A Inkster wrote:
>> So RDFa, as it is currently defined, does need a CURIE binding
>> mechanism. XML namespaces are used for XHTML+RDFa 1.0, but given that
>> namespaces don't work in HTML, an alternative mechanism for defining
>> them is expected, and for consistency would probably be allowed in  
>> XHTML
>> too - albeit in a future version of XHTML+RDFa, as 1.0 is already
>> finalised. (I don't speak for the RDFa task force as I am not a  
>> member,
>> but I would be surprised if many of them disagreed with me strongly  
>> on
>> this.)
>
> Speaking as an RDFa Task Force member - we're currently looking at an
> alternative prefix binding mechanism, so that this:
>
> xmlns:foaf="http://xmlns.com/foaf/0.1/"
>
> could also be declared like this in non-XML family languages:
>
> prefix="foaf=http://xmlns.com/foaf/0.1/"
>
> The thought is that this prefix binding mechanism would be available  
> in
> both XML and non-XML family languages.

Considering recent messages in this thread, using full URIs and  
refraining from declaring 'http' as a namespace prefix in XHTML would  
be more backwards compatible than minting a new attribute called  
'prefix'. (I haven't verified the test results about using full URIs  
myself.)

Even though switching over to 'prefix' in both HTML and XHTML would  
address the DOM Consistency concern, using them for RDF-like URI  
mapping would as opposed to XML names would remove the issue of having  
to pass around compound values and putting them on the same layer on  
the layer cake would remove most objections related to qnames-in- 
content, some usual problem with Namespaces in XML would remain:
  * Brittleness under copy-paste due to prefixes potentially being  
declared far away from the use of the prefix in source.
  * Various confusions about the prefix being significant.
  * The problem of generating nice prefixes algorithmically without  
maintaining a massive table of a known RDF vocabularies.
  * Negative savings in syntax length when I given prefix is only used  
a couple of times in a file.

> The reason that we used xmlns: was because our charter was to
> specifically create a mechanism for RDF in XHTML markup. The XML folks
> would have berated us if we created a new namespace declaration
> mechanism without using an attribute that already existed for exactly
> that purpose.

The easy way to avoid accusations of inventing another declaration  
mechanism is not to have a declaration mechanism.

URIs already have namespacing built into their structure. You seem to  
be taking as a given that there needs to be an indirection mechanism  
for declaring common URI prefixes. As far as I can tell, an  
indirection mechanism isn't a hard requirement flowing from the RDF  
data model. After all, N-Triples don't have such a mechanism.

> That being said, we're now being berated by the WHATWG list for doing
> the Right Thing per our charter... sometimes you just can't win :)

Groups have a say on what goes into their charter, so it's not like a  
group is powerlessly following a charter forced upon it entirely from  
the outside. :-)

> I don't think that the RDFa Task Force is as rigid in their  
> positions as
> some on this list are claiming... we do understand the issues, are
> working to resolve issues or educate where possible and desire an open
> dialog with WHATWG.

Great!

-- 
Henri Sivonen
hsivonen at iki.fi
http://hsivonen.iki.fi/