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Re: federated query question

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Tue, 24 May 2011 02:18:27 -0400
Message-ID: <4DDB4DB3.9050909@thefigtrees.net>
To: Carlos Buil Aranda <cbuil@fi.upm.es>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
Carlos, I've modified this note as discussed. Please confirm if the 
current text is OK with you.

thanks,
Lee

On 5/12/2011 12:29 PM, Carlos Buil Aranda wrote:
> yes, that's the point, to suggest the implementations to use some
> specific order not to fail when using a variable in the endpoint
> address. If not, the correct execution of the query can't be guaranteed.
>
> Carlos
>
> 2011/5/12 Lee Feigenbaum <lee@thefigtrees.net <mailto:lee@thefigtrees.net>>
>
>     I'm reviewing the latest set of changes.
>
>     In the section on boundedness (2.4) there is this note:
>
>     """
>     Note that this condition does not capture passing bindings between
>     SERVICE pattern, e.g. in
>       { ?X :p :o SERVICE ?X { ?Y :p :o } SERVICE ?Y { ?Z :p :o } },
>     SERVICE ?Y {...} is not service-safe, since ?Y is not strongly
>     bounded here. In order to capture the previous case, either SERVICE
>     semantics have to be order-dependent, or the engine has to determine
>     an implicit order of SERVICE calls that guarantees passing binding
>     in the right-order:
>       { ?X :p :o SERVICE ?Y { ?Z :p :o } SERVICE ?X { ?Y :p :o } }
>
>     The above query can be "emulated" with a nested SERVICE call as follows:
>
>       { ?X :p :o SERVICE ?X { ?Y :p :o SERVICE ?Y { ?Z :p :o } } }
>
>     This only works if the called services support (nested) SERVICE
>     patterns.
>
>     """
>
>     If I understand correctly, the intent of our current effort at
>     including the notion of strongly bound is to prohibit a query that
>     uses SERVICE like this. Is this correct? If so, I will change the
>     wording to reflect this and to suggest that implementations might
>     extend SERVICE by detecting an execution order that guarantees
>     variables used with SERVICE are strongly bound.
>
>     thanks,
>     Lee
>
>
Received on Tuesday, 24 May 2011 06:18:56 GMT

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