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Re: Blank nodes as subject maps in R2RML

From: Tomasz Pluskiewicz <tomasz.pluskiewicz@gmail.com>
Date: Wed, 25 Jul 2012 19:24:10 +0200
Message-ID: <CAAFOhSdh6JxSRnxu3bXm9Tp16nDHdR45f-bUSUd2Q0nUuC_acg@mail.gmail.com>
To: Juan Sequeda <juanfederico@gmail.com>
Cc: Richard Cyganiak <richard@cyganiak.de>, David McNeil <dmcneil@revelytix.com>, public-rdb2rdf-comments@w3.org
It is what I have asked last month on
http://answers.semanticweb.com/questions/16823/blank-nodes-as-subject-maps-in-r2rml

Indeed it is for direct mapping, which I implement using a default
mapping generator. Though I am still unsure how a subject map should
look like for a direct mapping such as in
http://www.w3.org/2001/sw/rdb2rdf/test-cases/#D005-1table3columns3rows2duplicates
test case. It does indeed seem that each tuple generates a fresh blank
node. If it were to only contain rr:termType and rr:class, then it is
invalid in the light of current specifications as Richard notes.

Otherwise I would like to ask for guidance what should such default
mapping look like.

Regard,
Tomasz Pluskiewicz

On Wed, Jul 25, 2012 at 7:05 PM, Juan Sequeda <juanfederico@gmail.com> wrote:
> However, If this were to be valid, it would automatically generate a fresh
> bnode for each tuple. Which would lead us to the whole discussion that we
> had before about bnodes and the direct mapping.
>
> Tomasz, is this a feature or something that you need?
>
> Juan Sequeda
> +1-575-SEQ-UEDA
> www.juansequeda.com
>
>
>
> On Wed, Jul 25, 2012 at 11:59 AM, Richard Cyganiak <richard@cyganiak.de>
> wrote:
>>
>> 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 17:25:19 UTC

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