On 5 Jun 2007, at 07:32, Andrew Newman wrote:
On 6/5/07, Steve Harris <[EMAIL PROTECTED]> wrote:
On 5 Jun 2007, at 06:55, Andrew Newman wrote:
> On 6/5/07, Steve Harris <[EMAIL PROTECTED]> wrote:
> 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.
So OUTER JOIN is a set operation not a join operation - so they are
differently scoped in SQL too (I think).
Yes, well put, but that was my point: you can't have some variables
that are scoped and some that are not in SQLs UNION, you can in SPARQLs.
- Steve
