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Re: issues in rq25

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Thu, 25 Jan 2007 09:57:44 +0000
Message-ID: <45B87F18.3040108@hp.com>
To: Eric Prud'hommeaux <eric@w3.org>
CC: public-rdf-dawg@w3.org



Eric Prud'hommeaux wrote:
> * Seaborne, Andy <andy.seaborne@hp.com> [2007-01-24 20:15+0000]
>>
>> Eric Prud'hommeaux wrote:
...
>>> 7 Matching Alternatives
>>>
>>>  Query results involving a pattern containing GP1 and GP2 will
>>>  include separate solutions for each match where GP1 and GP2 give
>>>  rise to *different* sets of bindings.
>>>
>>> We talked about this some, too. Can't remember where we got. I prefer
>>> to not have an implicit DISTINCT on UNION (something the SQL folks
>>> regret).
>>
>> See the algebra:
>> http://www.w3.org/2001/sw/DataAccess/rq23/rq25-algebra.html#defn_algUnion
>>
>> The cardinality in union is the sum of left and right cardinalities.
> 
> ok, i hacked at the UNION text:
> 
>   Query results of GP1 <code>UNION</code> GP2 are all of the 
>   solutions from GP1 and the solutions from GP2, in any order.
> 
> Still not ideal as it leaves the possibility that the results are
> either
> 
> GP1a
> GP1b
> GP1c
> GP2a
> GP2b
> GP2c
> or
> GP2a
> GP2b
> GP2c
> GP1a
> GP1b
> GP1c
> 
> vs
> GP2b
> GP2c
> GP1a
> GP1c
> GP2a
> GP1b
> 
> but perhaps good enough as there is nothing saying that there is any
> order to the constituent results.

We really ought not to say anything about order - I can think of two 
reasonable implementation schemes that will give different orders (an 
index-scan based one and a recursive evaluation one).

	Andy
Received on Thursday, 25 January 2007 09:57:52 GMT

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