ISSUE-41 What are the options?

Reading the extensive discussion on ISSUE-41, there seem to be three options on
how to handle SQL NULLs in the database:

A)  Do not generate triples for NULLs
B)  Define a special values such as RDB2RDF:NULL to represent a NULL
c)  Use a blank node to represent a NULL

As Souri pointed out on the call and Juan in mail, option A) does not lose information
as long as you have a RDF Schema.  Alexandre points out that DM does implicitly
define a RDF Schema and I think R2R also, implicitly, defines a RDF Schema.  So, I
would argue that A) does not lose information.

The problem with B) is that it defines a new "value" and the SQL NULL is not really
a "value".  It has special semantics such as "NULLs cannot be joined with each other."
Richard has pointed out other problems with translating NULL to a special value.

Re. C) I confess I do not understand bNodes very well.  The RDF documents refer to them
as existential variables which seems just different from a representation for SQL NULLs.

Does this makes sense?  Are there other options?
All the best, Ashok

Received on Wednesday, 18 May 2011 13:15:23 UTC