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

From: Pierre-Antoine Champin <swlists-040405@champin.net>
Date: Wed, 21 May 2008 09:03:44 +0200
Message-ID: <4833C950.6060301@champin.net>
CC: Semantic Web <semantic-web@w3.org>

Peter Ansell a écrit :
> 2008/5/21 Pierre-Antoine Champin <swlists-040405@champin.net>:
>> Bernard Vatant a écrit :
>>> 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
>> May be I don't understand your problem well, but it seems to me that there
>> is another way of "closing" the world in this particulat context : using a
>> *functional* property :closingDays, and have its value be an rdf:List
>> collection, which in Turle/SPARQL is written :
>> :WidgetMuseum   :openingPeriod   _:p1
>> _:p1      :begins       2008-03-01
>> _:p1      :ends         2008-10-31
>> _:p1      :closingDays  (:Tuesday :Sunday)
>> Whether this structure is easy to query with SPARQL, I'm not sure... But it
>> seems to me that it makes your knowledge about opening and closing days
>> complete.
> RDF Collections, including List's are defined to be complete [1], so
> that may be one way of getting around the open world assumption, but
> how would you imply that a given day was valid and still not in the
> closingDays List? Do you have to create another List for openingDays,
> which would limit this ability to cases where you know everything?

my guess is that the "negation by failure", with the !bound(?u) trick
would do it.
Informally, a day is valid iff it (as a date) is between :begins and
:ends, and it (as a day of week) does not belong to the :closingDays.

But once again, I'm not sure how easy it is to formalize that informal
query in SPARQL. My point was more about the open/closed world problem...

Received on Wednesday, 21 May 2008 07:04:21 UTC

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