  We investigate the data exchange from relational databases to RDF graphs
inspired by R2RML with the addition of target shape schemas. We study the
problems of consistency i.e., checking that every source instance admits a
solution, and certain query answering i.e., finding answers present in every
solution. We identify the class of constructive relational to RDF data exchange
that uses IRI constructors and full tgds (with no existential variables) in its
source to target dependencies. We show that the consistency problem is
coNP-complete. We introduce the notion of universal simulation solution that
allows to compute certain query answers to any class of queries that is robust
under simulation. One such class are nested regular expressions (NREs) that are
forward i.e., do not use the inverse operation. Using universal simulation
solution renders tractable the computation of certain answers to forward NREs
(data-complexity). Finally, we present a number of results that show that
relaxing the restrictions of the proposed framework leads to an increase in
complexity.
