some r2rml questions

I see this list has no traffic for several months but I thought I would
try here first. If anyone knows of a more active forum for discussion,
please advise.

I've run into a couple of issues implementing an R2RML processor, and I
wondered if others have encountered these and if so would you share some
thoughts on how to solve them.

First, I want to transform a column value in the R2RML processor, rather
than in SQL, because it is quite inconvenient to do it in SQL. I would
like the R2RML mapping spec to specify the value transformation. My
solution was to add a "columnValueConstructor" predicate to the Term
Map, with a range of values restricted to id values known to the R2RML
processor. The handlers for each column value constructor must be
hardcoded into the R2RML processor. While this suits my purpose, it is
obviously not completely general or easily extensible. Ideally there
might be a standard ValueMap construct that could either be defined by a
well-known ID or an actual function specification of some sort. A
reference to a ValueMap inside a term map would tell the processor to
transform the column value before emitting it as RDF.

Second, I want to conditionally emit a predicate and object for a
subject, depending on the column value returned from the object map. I
can imagine a workaround by defining appropriate SQL views in the
mapping spec, but in some cases it would seem more efficient and
transparent to place a guard condition on a PredicateObjectMap.

I would appreciate any comments on these issues.

Regards,
--Paul

Received on Thursday, 14 March 2013 00:47:25 UTC