Proposal: No DM change; R2RML defines default mapping

Eric maintains his objection to allowing a non-cardinality-preserving option of the DM for compatibility with R2RML.

A possible way forward is to leave the DM as is, and define the non-cardinality-preserving option *in the R2RML spec*, with normative reference to the DM. The R2RML spec would say explicitly that this relaxed variant of the DM is *only* intended as a default mapping for R2RML.

Proposed wording to make this happen is below. Note that the entire proposal is MAY, that is, conforming R2RML processors don't have to do anything new, and implementers who don't care about this whole default mapping business can ignore it (as it should be).

This is very similar to the Proposal A from last week, it just moves the text that defines the non-c9y-preserving option from one spec to the other.

Best,
Richard



== 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.
]]



== 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.
]]

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

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

Received on Tuesday, 15 May 2012 19:51:45 UTC