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Re: second review of json-ld

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Fri, 29 Mar 2013 17:33:49 +0000
Message-ID: <5155D07D.6030807@epimorphics.com>
To: public-rdf-wg@w3.org


On 29/03/13 17:21, Gregg Kellogg wrote:
>
> Gregg Kellogg
> gregg@greggkellogg.net <mailto:gregg@greggkellogg.net>
>
> On Mar 29, 2013, at 8:24 AM, Sandro Hawke <sandro@w3.org
> <mailto:sandro@w3.org>> wrote:
>
>> ...
>>
>> Alas, there is no defined way to merge RDF datasets.
>>
>> The problem is that sometimes it's obvious that the merge of
>>     <g> { <a> <b> 1 }
>> and
>>     <g> { <a> <b> 2 }
>> is
>>     <g> { <a> <b> 1,2 }
>> and sometimes it's obvious the two can't be merged because they
>> contradict each other.

The same is true of two graphs from different times:

<here> :currentTemperature "hot" .

and

<here> :currentTemperature "cold" .

Merge is a low-level mechanism - it may be suitable or not.

re: bnodes:
The scope/bnodes proposals may help.

	Andy

>>
>> See: http://www.w3.org/2011/rdf-wg/track/issues/17
>> RESOLVED: close issue-17
>> <http://www.w3.org/2011/rdf-wg/track/issues/17> -- there is no general
>> purpose way to merge datasets; it can only be done with external
>> knowledge.
>>
>> Proposed solution is to define it here, something like:  If multiple
>> embedded JSON-LD documents are extracted as RDF, the result is a
>> dataset formed by merging all the graphs that have the same name (and
>> thus making a single named graph per graph name) and all the default
>> graphs (to make one resulting default graph).
>>
> I discussed this on the GitHub issue tracker too.
>
> We had a discussion on IRC about the problems of merging default graphs.
> For example, if a developer re-states the facts in both RDFa and JSON-LD
> in the same document (worse, microdata, which almost encourages the use
> of BNodes), the result will be a merger with duplicate BNodes, that
> typically are intended to be exactly the same node.
>
> One way would be to provide an algorithm for creating a named graph to
> contain the default graphs of all included script, microdata or RDF/XML
> which is also extracted (another case where BNode graph IDs would have
> been useful). Alternatively, a Note on the subject could just warn
> against this pattern.
>
> Alternatively, the result could simply be a set of graphs and datasets
> where there is no defined merger, leaving it up to the application;
> however, I don't find this very satisfying.
>>
>> ...
>>
>>     -- Sandro
>>
> Gregg
Received on Friday, 29 March 2013 17:34:27 UTC

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