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Re: Proposal for ISSUE-11: Default prefix declarations

From: Shane McCarron <shane@aptest.com>
Date: Sun, 28 Feb 2010 21:58:34 -0600
Message-ID: <4B8B3B6A.8080609@aptest.com>
To: Manu Sporny <msporny@digitalbazaar.com>
CC: RDFa WG <public-rdfa-wg@w3.org>
+1.  The only risk I see associated with this proposal is that people 
might assume that some prefix is pre-declared when in fact it is not 
(e.g., my favorite vocab is skiing: - that MUST be in there). 

Manu Sporny wrote:
> One of the criticisms of RDFa 1.0 is that certain snippets may fail
> under cut and paste scenarios. This criticism comes from two directions:
>
> 1. It has been asserted that the xmlns: syntax for prefix declaration
>    is confusing and that authors may not use it correctly.
> 2. It has been asserted that authors may haphazardly copy-and-paste
>    popular RDFa markup such as SIOC, FOAF or Dublin Core terms.
>
> So, for example, an author may take this:
>
> <div xmlns:dc="http://purl.org/dc/elements/1.1/">
>    ...
>    <div about="/alice/posts/trouble_with_bob">
>       <h2 property="dc:title">The trouble with Bob</h2>
>       <h3 property="dc:creator">Alice</h3>
>       ...
>    </div>
>
> and copy-and-paste just this part into their document:
>
>    <div about="/alice/posts/trouble_with_bob">
>       <h2 property="dc:title">The trouble with Bob</h2>
>       <h3 property="dc:creator">Alice</h3>
>       ...
>    </div>
>
> This copy-paste error in RDFa 1.0 would result in no triples being
> generated because the "dc:" prefix is undefined. The author forgot to
> copy the xmlns:dc="..." declaration.
>
> We could address the most common markup errors by defining a list of
> default URI mappings, for example:
>
> """
> The list of default URI mappings is:
>
>    rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#
>    rdfs: http://www.w3.org/2000/01/rdf-schema#
>    dc: http://purl.org/dc/terms/
>    foaf: http://xmlns.com/foaf/0.1/
> """
>
> We would then modify the initialization of the RDFa Processor in Section
> 5.5: Sequence[1] from this:
>
> """
>    the list of URI mappings is empty;
> """
>
> to this:
>
> """
>    this list of URI mappings is set to the list of default URI mappings;
> """
>
> The default list of URI mappings can be overwritten during operation of
> the processing rules. So, if the author re-defines the "dc" prefix in
> the current context to another value, the new value would be used to
> generate triples in the current context.
>
> Note that this proposal does not attempt to determine the ideal list of
> default URI mappings. That would be best accomplished by using the "top
> N list of most commonly requested vocabularies" on prefix.cc[2], getting
> prefix usage data from Google or Yahoo, or using another data-driven
> approach that can be done at a later time. Preferably, we would wait
> until just before Last Call to finalize the list of default URI mappings.
>
> Also note that another benefit of this proposal is that the author will
> not need to declare prefix mappings using xmlns: for the most commonly
> used RDFa prefixes.
>
> -- manu
>
> [1] http://htmlwg.mn.aptest.com/rdfawg/rdfa-core/#sequence
> [2] http://prefix.cc/
>
>   

-- 
Shane P. McCarron                          Phone: +1 763 786-8160 x120
Managing Director                            Fax: +1 763 786-8180
ApTest Minnesota                            Inet: shane@aptest.com
Received on Monday, 1 March 2010 03:59:20 GMT

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