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Re: Blank nodes as subject maps in R2RML

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 25 Jul 2012 17:59:45 +0100
Cc: Juan Sequeda <juanfederico@gmail.com>, David McNeil <dmcneil@revelytix.com>, public-rdb2rdf-comments@w3.org
Message-Id: <20379CE4-CE88-46DF-8178-55C0AEE9FB8A@cyganiak.de>
To: Tomasz Pluskiewicz <tomasz.pluskiewicz@gmail.com>
On 25 Jul 2012, at 15:05, Tomasz Pluskiewicz wrote:
> Sorry to revive an old topic, but I have recenlty realized the root of
> my question.
> 
> The R2RML specs at http://www.w3.org/TR/r2rml/#dfn-term-map state
> clearly that "A term map must be exactly one of the following: a
> constant-valued term map, a column-valued term map, a template-valued
> term map." Doesn't this mean that a term map
> 
> <StudentsTriplesMap> rr:subjectMap
> [
>    rr:termType rr:BlankNode;
>    rr:class <http://example.com/Student>
> ];
> 
> is in fact invalid, having no explicit rr:constant, rr:column or
> rr:template property?

It is indeed invalid. You'd usually want an rr:template or rr:column that creates the blank node identifier.

Best,
Richard


> 
> Regards,
> Tomasz
> 
> On Fri, Jun 8, 2012 at 10:19 PM, Tomasz Pluskiewicz
> <tomasz.pluskiewicz@gmail.com> wrote:
>> Thank you for answering. Also, let me answer here again.
>> 
>> I forgot to mention I intended the mapping as default mapping for
>> table without primary key.
>> 
>> In my oppinion by default direct mapping should generate a blank node
>> for each row. And I do have mixed feelings about the behavior not
>> preserving duplicate rows.
>> 
>> Regards,
>> Tomasz
>> 
>> On Fri, Jun 8, 2012 at 6:26 PM, Juan Sequeda <juanfederico@gmail.com> wrote:
>>> I asked on the forum, but let me ask here.
>>> 
>>> are you expecting the R2RML engine to generate a blank node for each tuple,
>>> or do you have a column value that you would like to use in order to
>>> generate the blank node?
>>> 
>>> Juan Sequeda
>>> +1-575-SEQ-UEDA
>>> www.juansequeda.com
>>> 
>>> 
>>> 
>>> On Fri, Jun 8, 2012 at 9:22 AM, David McNeil <dmcneil@revelytix.com> wrote:
>>>> 
>>>>> From the latest R2RML draft:
>>>> 
>>>> * a subject map is a term map,
>>>> http://www.w3.org/2001/sw/rdb2rdf/r2rml/#dfn-term-map
>>>> 
>>>> * the termType property can be used on term maps,
>>>> http://www.w3.org/2001/sw/rdb2rdf/r2rml/#termtype
>>>> 
>>>> So "yes", you can use termType on subject maps and this is how you would
>>>> produce subjects as blank nodes.
>>>> 
>>>> -David
>>> 
>>> 
> 
Received on Wednesday, 25 July 2012 17:00:42 UTC

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