ISSUE-25 (Direct mapping in custom mappings): Including direct mapping constructs in R2RML mappings

ISSUE-25 (Direct mapping in custom mappings): Including direct mapping constructs in R2RML mappings

http://www.w3.org/2001/sw/rdb2rdf/track/issues/25

Raised by: David McNeil
On product: 

The R2RML editor's draft, http://www.w3.org/2001/sw/rdb2rdf/r2rml/#sql-conformance, identifies this issue:

"The use of a 'convention over configuration' approach has been proposed, where a mapping is not expressed completely, but rather as a delta from the default mapping. In other words, only those parts that one wants to be different from the default mapping have to be written down in the mapping file."

An approach has been discussed in which a custom mapping can specify that the direct mapping should be used for some database elements. This would "expand" in the custom mapping and provide the direct mapping defined constructs without requiring the user to define them explicitly.

While I can see the benefit of this approach I think it would be better to start with a simpler specification that does not tie the R2RML specification to the Direct Mapping specification in this way. This provides several benefits:

* R2RML mappings are easier to understand (the Direct Mapping specification does not need to be referenced to understand a custom mapping)
* R2RML is easier to implement without the ties to the Direct Mapping
* it is easier to implement R2RML in a consistent manner (differences in interpretation of the Direct Mapping spec do not leak into the implementation of R2RML itself)
* this keeps contentious issues related to automatic blank node generation and URI generation out of R2RML (otherwise these issues leak into R2RML via the Direct Mapping support)
* this approach allows the W3C, users, and vendors the chance to gain more experience with R2RML mappings before attempting to define standard default mappings that are a part of R2RML

Received on Tuesday, 1 March 2011 14:56:18 UTC