Re: Minimalist proposal to resolve no-primary-key issue

Yes, I am proposing an alternative.  I have some problems with Richard's wording.  I've added comments inline.
They are in Red

Changes in the Direct Mapping ==

http://www.w3.org/TR/2012/CR-rdb-direct-mapping-20120223/

REMOVE:
[[
The Direct Mapping is intended to provide a default behavior for R2RML: RDB to RDF Mapping Language [R2RML].
]]

ADD as new paragraph to end of Section 1 Introduction:
[[
This specification has a companion, the R2RML mapping language [R2RML], that allows the creation of customized mapping from relational data to RDF. R2RML defines a relaxed variant of the Direct Mapping intended as a default mapping for further customization.
]]

[AM] I don't understand the last sentence.  What does "relaxed variant" mean.  I tried to be specific.


== Changes in R2RML ==

http://www.w3.org/2001/sw/rdb2rdf/r2rml/

ADD a new section:
[[
4.4 Default Mapping

An R2RML processor MAY include an*R2RML default mapping generator*. This is a facility that introspects the schema of the input database and generates a*default mapping document*  intended for further customization by a mapping author. The R2RML mapping expressed in the default mapping document SHOULD be such that its output is the Direct Graph [DM] corresponding to the input database.

Duplicate row preservation: For tables without a primary key, the Direct Graph requires that a fresh blank node is created for each row. This ensures that duplicate rows in such tables are preserved. This requirement is relaxed for R2RML default mappings: They MAY re-use the same blank node for multiple duplicate rows. This behaviour does not preserve duplicate rows. Implementations that provide default mappings based on the Direct Graph MUST document whether they preserve duplicate rows or not.
]]

[AM] I don't see what the first paragraph adds.  If we agree to add only the second para I'm ok.

Add a bullet point to the list of defined artefacts in Section 3 Conformance:
[[
   . R2RML default mapping generators
]]

[AM] I don't think we need this

Move [DM] from C.2 Other References to C.1 Normative References



All the best, Ashok

On 5/15/2012 3:26 PM, David McNeil wrote:
> On Tue, May 15, 2012 at 5:19 PM, ashok malhotra <ashok.malhotra@oracle.com <mailto:ashok.malhotra@oracle.com>> wrote:
>
>     I think we just need to fix the DM.  If you disagree, please indicate what else needs to be said.
>
>     The DM spec says:
>     [[The Direct Mapping is intended to provide a default behavior for R2RML: RDB to RDF Mapping Language <http://www.w3.org/TR/2012/CR-r2rml-20120223/> [R2RML] <http://www.w3.org/TR/rdb-direct-mapping/#R2RML>. It can also be used to materialize RDF graphs or define virtual graphs, which can be queried by SPARQL or traversed by an RDF graph API.]]
>
>     Add an asterisk after the first sentence and a footnote.  The footnote says:
>     [[Except in the case of tables or views without a primary key.  In this case, identical rows may be kept distinct
>     by the DM and collapsed into a single row by R2RML]]
>
>
> Ashok - Are you proposing this as an alternative to what Richard wrote in his email today with the subject "Proposal: No DM change; R2RML defines default mapping"? I am curious what prompted you to come up with another proposal.
>
> -David