On 5 Jun 2007, at 06:55, Andrew Newman wrote:
On 6/5/07, Steve Harris <[EMAIL PROTECTED]> wrote:
if that works then you have a bug. The behaviour of SPARQLs UNION
is not
very natural from a relation algebra p.o.v., and this may have
confused
developers familiar with that.
Isn't it just outer union? And isn't outer union just part of SQL 92.
And isn't SQL 92 implemented by most (all?) databases.
In a sense. You can expand any SPARQL UNION into a set of SQL UNIONs,
but SQLs UNION doesn't allow you to explicitly write
:x :y ?z { ?z :p ?q } UNION { ?z :r ?q }
where the ?z-s are scoped to the whole expression and the ?q-s are
scoped to the block. In relational the equivalent would be to join
two expressions, each of two joins and use rho to unify the
variables. But, I personally wouldn't write it that way.
- Steve
