Re: ISSUE-29: Require blank node and IRI identifier expressions to produce strings

[Copy of a note I added here:
http://www.w3.org/2001/sw/rdb2rdf/track/issues/29]

Yesterday on the working group conference call we discussed the option of
not requiring the expressions to be strings, but requiring that they be of a
type that can be converted to a string in a canonical (unambiguous) manner.
I think this is a promising approach that achieves the same goal as this
issue originally described. Whether they are strings or whether they are
unambiguously convertible to a string seems that either meets the goal of
allowing them to be used as strings.

-David