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Re: Open world issue (opening vs closing days) and SPARQL CONSTRUCT

From: Bernard Vatant <bernard.vatant@mondeca.com>
Date: Tue, 20 May 2008 18:27:50 +0200
Message-ID: <4832FC06.1090906@mondeca.com>
To: Ivan Mikhailov <imikhailov@openlinksw.com>
Cc: Semantic Web <semantic-web@w3.org>, Florence Amardeilh <florence.amardeilh@mondeca.com>, Steph <steph.weiser@gmail.com>, Philippe Laublet <Philippe.Laublet@paris4.sorbonne.fr>

Hi Ivan

> Bernard,
>
> My personal way of thinking about logic in open world is to treat a fact
> _:p1 :closingDay :Tuesday as an conjunction of two: "Tuesday is a
> closing day for _:p1" and "I know that Tuesday is a closing day for
> _:p1". so the negation of that fact is "Tuesday is not a closing day for
> _:p1 or I don't know that Tuesday is a closing day for _:p1".
>   
In the "pragmatic open world", I would assume the former holds 
until/unless the information source cries otherwise, or clients provide 
angry feedback because they found the doors closed on Tuesday.
> Similarly, aggregates are a problem. "Select exact count of X" of SQL is
> much more useful than "Select a count of known instances of X so it
> might be used as a guess of actual count" in a open world.
>
> Sometimes the SPARQL world is closed, or partially closed. This is the
> case when part of data come from closed sources such as relational
> databases. When a SPARQL processor can access relational data directly,
> such as OpenLink Virtuoso ( http://virtuoso.openlinksw.com ), the
> negation becomes "more meaningful" as well as aggregates. That's why
> Virtuoso extends SPARQL for business intelligence whereas W3C SPARQL
> does not. W3C Data Access Working Group did not extend SPARQL with
> features that are not required in most of open world applications (or
> required but unsafe for newbie) .
>
> The conclusion. Yes, your case can be handled by something like
>
> CONSTRUCT { ?s :openingDay ?dayofweek }
> WHERE
>   {
>     :WidgetMuseum   :openingPeriod ?s
>     ?s :begins 2008-03-01 .
>     ?s :ends        2008-10-31 .
>     ?dayofwee a somedictionary:dayOfWeek .
>     OPTIONAL { ?s2 :closingDay ?dayofweek . FILTER (?s2 = ?s) }
>     FILTER (!bound (?s2))
>   }
>   
Found something of the like in paper quoted by Stefen, and even in the 
SPARQL specification itself, under the title "negation by failure".
Not sure I've completely understood yet how it can work, in particular 
the semantics of ?s2
Any further explanation welcome ...

Bernard

> but that's still "construct a super-set of the right result" while the
> world is open :)
>
> The query demonstrates one more headache, common for SQL and SPARQL --
> there's no way to enumerate Monday, Tuesday ... Sunday right in the
> query, there's a need in an external enumeration.
>
> Best Regards,
>
> Ivan Mikhailov,
> OpenLink Software.
>
> On Mon, 2008-05-19 at 23:17 +0200, Bernard Vatant wrote:
>   
>> Hi all
>>
>> We're currently fighting with knowledge extraction about opening/closing 
>> days for tourism facilities (hotels, restaurants, museums, campings ...).
>> Information can be found in terms of closing and/or opening days during 
>> a period, such as :
>> "Widget Museum is open in 2008, from March 1st to October 31st, closed 
>> on Sunday and Tuesday".
>> NLP can extract the following description (1)
>>
>> :WidgetMuseum   :openingPeriod   _:p1
>> _:p1      :begins     2008-03-01
>> _:p1      :ends        2008-10-31
>> _:p1      :closingDay      :Tuesday
>> _:p1      :closingDay      :Sunday
>>
>> In an open world, we have no way to know if this is a complete 
>> description, and can't infer that Widget Museum is open on Monday.
>>
>> The other way round, if the information is given in terms of opening days,
>> "Widget Museum is open in 2008, from March 1st to October 31st, on 
>> Monday, Wednesday, Thursday, Friday and Saturday".
>> Which yields the description (2)
>>
>> :WidgetMuseum   :openingPeriod   _:p2
>> _:p2      :begins     2008-03-01
>> _:p2      :ends        2008-10-31
>> _:p2      :openingDay      :Monday
>> _:p2      :openingDay      :Wednesday
>> _:p2      :openingDay      :Thursday
>> _:p2      :openingDay      :Friday
>> _:p2      :openingDay      :Saturday
>>
>> ... we can't infer that Widget Museum is closed on Tuesday and Sunday. 
>> IOW there is no way to identify logically _:p1 and _:p2 in an open world.
>>
>> Supposing (1) is the standard target description required by the 
>> ontology used in the system, I thought possible to write, in our closed 
>> world, a SPARQL CONSTRUCT query which would yield (1) from (2).
>> But thinking twice, my hunch is now that it is impossible, because of 
>> the implicit open world assumption made by SPARQL.
>>
>> Has someone already dealt with such issues? Any pointer welcome.
>>
>> Thanks for your help
>>
>> Bernard
>>
>>     

-- 

*Bernard Vatant
*Knowledge Engineering
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*Mondeca**
*3, citÚ Nollez 75018 Paris France
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Received on Tuesday, 20 May 2008 16:28:44 GMT

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