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Re: the LHS of OPTIONAL

From: Steve Harris <steve.harris@garlik.com>
Date: Thu, 23 Nov 2006 17:46:34 +0000
Message-Id: <7CFC119D-CB39-430D-9FB5-4EDA54400027@garlik.com>
Cc: public-rdf-dawg@w3.org
To: Fred Zemke <fred.zemke@oracle.com>


On 23 Nov 2006, at 17:37, Fred Zemke wrote:

>
> { T1 .
> T2 . }
> OPTIONAL { T3 }
> OPTIONAL { T4 }
> OPTIONAL { T5 }

I still prefer it without the extra {}s.

> and the query processor can effectively supply the rest
> as shown in your expansion.
>
>>
>> Plus, explaining, and implementing the difference between:
>>
>> { T1 . T2 . } OPTIONAL { T3 }
>>
>> and
>>
>> T1 . { T2 } OPTIONAL { T3 }
>>
>> is not something I relish.
>
> On that we have no choice, since both are presumably legal
> in the language, whether we adopt my suggestion or not.

Yes, though they may or may not mean different things. I'm not clear  
on that.

My engine treats both of those as

T1 . T2 . OPTIONAL { T3 }

which I suspect is not correct. Eg. if T1 fails, but T2 succeeds  
should the OPTIONAL be attempted? If T1 fails in my engine then T2  
and the OPTIONAL will be shortcutted.

- Steve
Received on Thursday, 23 November 2006 17:46:36 GMT

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