- From: Steve Harris <swh@ecs.soton.ac.uk>
- Date: Tue, 5 Jun 2007 08:18:18 +0100
- To: "Andrew Newman" <andrewfnewman@gmail.com>
- Cc: public-sparql-dev@w3.org
On 5 Jun 2007, at 07:32, Andrew Newman wrote:
>
> On 6/5/07, Steve Harris <swh@ecs.soton.ac.uk> wrote:
>> On 5 Jun 2007, at 06:55, Andrew Newman wrote:
>> > On 6/5/07, Steve Harris <swh@ecs.soton.ac.uk> 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
Received on Tuesday, 5 June 2007 07:20:24 UTC