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Re: Keeping R2RML free of Direct Mapping dependency (ISSUE-25)

From: Ivan Herman <ivan@w3.org>
Date: Tue, 26 Apr 2011 15:35:16 +0200
Cc: RDB2RDF WG <public-rdb2rdf-wg@w3.org>
Message-Id: <CE7784AE-3F1B-4C0A-9EFB-122C8B944019@w3.org>
To: David McNeil <dmcneil@revelytix.com>

On Apr 26, 2011, at 15:27 , David McNeil wrote:

> 
> 
> On Tue, Apr 26, 2011 at 3:25 AM, Ivan Herman <ivan@w3.org> wrote:
> If the group decides not to make a reference to the Direct Mapping in in R2RML, then we still have to define what happens to those parts of the table that a specific R2RML file does not cover. In other words, we would have to define a default behaviour.
> 
> Ivan - Thanks for the response. The default behavior (as you described later in your message) would be to not map those entities to RDF. It is my understanding that this is what the current R2RML spec requires but I don't think this is explicitly stated.

It is certainly not. I remember asking this question at some of my earlier reviews, and that was never properly discussed or decided as far as I remember (but my memory is failing with age...)

> The closest I can find at a quick skim is section 1.4 "The output of an R2RML mapping is an RDF dataset. The RDF triples in the dataset are the result of applying the mapping rules of each TriplesMap to the rows of its logical table." I think this behavior (only mapping entities that have been explicitly mapped) is legitimate. The use cases that I have been working with require the R2RML mapper to have explicit control over what is mapped.
> 
> Even under the scheme that allows the Direct Mapping constructs to be invoked from an R2RML mapping I think that not mapping the entities would be the default behavior. It would only be if the R2RML mapping indicated "please use the Direct Mapping for RDB entity <X>" that the Direct Mapping would be used.

So... in my mind the first question we have to answer is whether we want an 'empty' default mapping or not. If not, than I believe the DM is a reasonable answer. If yes, then indeed there is no automatic DM mapping, but then your last approach allowing the author to declare in his/her R2RML mapping that the DM case should be used for the non-defined cells makes sense to me...

Ok. At least I understand where you come from:-)

Thanks

Ivan



> 
> -David
> 
> 


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Received on Tuesday, 26 April 2011 13:38:22 GMT

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