Conditional creation of property in R2RML - semantic-web

Question

I'm playing around with R2RML and I was wondering if I can create a property depending on the content of a RDB table cell.
The D2RQ mapping language has d2rq:condition that can handle that.
e.g.:
if value in column/table cell 'name' is 'abc' create property 'abc'
rr:predicateObjectMap [
rr:predicate ex:abc
rr:objectMap [
rr:column "name";
rr:datatype xsd:string;
# equivalent for d2rq:condition "name='abc'"
];
]
if value in column/table cell 'name' is 'xyz' create property 'xyz'
rr:predicateObjectMap [
rr:predicate ex:xyz
rr:objectMap [
rr:column "name";
rr:datatype xsd:decimal;
# equivalent for d2rq:condition "name='xyz'"
];
];
I couldn't find any suggestion in W3C's R2RML Recommendation.
Any ideas? :-)
Update:
I had the idea of using rr:sqlQuery
e.g.
rr:SQLQuery """
select (case TABLENAME.COLUMNNAME
when 'this' then 'propertyOne'
when 'that' then 'propertyTwo'
end) as VARIABLE_PREDICATE
from TABLENAME """;
and apply it to a rr:predicate or rr:predicateMap with
rr:predicateObjectMap [
rr:predicateMap [ rr:template "ex:{VARIABLE_PREDICATE}" ];
rr:objectMap [ rr:column "COLUMNNAME"; ];
];
But that didn't work. I guess predicateMaps can be rr:constants only and not rr:templates :( . At least the W3C Recommendation just shows constants within predicateMap.
Still searching for a solution... :/
P.S. I'm disappointed that a proprietary language like d2rq seems to be more powerful (at this point).

Answer 1

R2RML doesn't have conditional properties (like in D2RQ). The design was done on purpose in order not to complicate the language. Any type of "complex" mapping requires SQL.
A solution is the following:
#prefix rr: <http://www.w3.org/ns/r2rml#>.
<#Mapping> a rr:TriplesMap;
rr:logicalTable [ rr:SQLQuery """
select id, COLUMNNAME, (case TABLENAME.COLUMNNAME
when 'this' then 'http://ex.com/propertyOne'
when 'that' then 'http://ex.com/propertyTwo'
end) as VARIABLE_PREDICATE
from TABLENAME """; ];
rr:subjectMap [
rr:template "http://ex.com/foo/{id}";
];
rr:predicateObjectMap [
rr:predicateMap [ rr:column "VARIABLE_PREDICATE" ];
rr:objectMap [ rr:column "COLUMNNAME" ];
].

Answer 2

We routinely do that in mapping the Getty vocabs, for props that depend on key values (flags). Eg
<#ContribTermRelPreferred>
a rr:TriplesMap;
rr:logicalTable [ rr:sqlQuery """
SELECT ...
UDF_LOD_LOOKUP_PROPERTY('contrib_rels_term','preferred',CRT.PREFERRED) CONTRIBPREF
""" ];
rr:predicateObjectMap [
rr:predicateMap [ rr:column "CONTRIBPREF" ];
rr:objectMap [ rr:template "http://vocab.getty.edu/aat/contrib/{CONTRIB_ID}" ];
].