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Re: Non-global Keys

From: Jim Hendler <hendler@cs.umd.edu>
Date: Tue, 6 May 2003 22:33:30 -0400
Message-Id: <p05200f42bade20c90071@[10.0.1.2]>
To: Bob MacGregor <macgregor@ISI.EDU>
Cc: public-webont-comments@w3.org

Bob - thank you for your comment, the working group will consider it 
and get back to you
  -Jim H.



OWL ought to include a syntax for defining non-global
>keys.  For example, suppose the classes Employee and
>EmployeeHistory both share the attribute hasSSN.
>One would like to be able to assert that 'hasSSN' is
>a key for instances of Employee, but not for instances
>of EmpoyeeHistory.  InverseFunctionalProperty does not
>permit this.
>
>Currently, single valued restrictions on properties
>can be stated globally or with respect to instances
>of a Class.  Similarly, range restrictions on properties
>can be stated globally, or with respect to instances
>of a Class.  By analogy, keys should have similar
>flexibility.
>
>The property we have in mind for specifying a key
>would have domain Class and range Property.  One
>might call it something like 'hasKey' or 'classHasKey'.
>However, if we are broad-minded, we will recognize
>that sooner or later we will also want to support
>compound keys.  So perhaps it could be called
>'hasSimpleKey' or 'hasAtomicKey'.
>
>When n-ary relational tables are converted into RDF
>format, each table maps to a class and each of a table's
>columns maps to a property.  If a table has
>a compound key (a rather common-place occurrence),
>then one would like to be able to map its key
>restriction to RDF as well.  That would require
>that we support the notion of a compound key.  For
>example, the class EmployeeHistory might have the
>key <hasSSN, historyDate>.
>
>A property representing a compound key declaration
>might map a Class to a List.  Perhaps this property
>could be called 'hasCompoundKey'.
>
>Provisions for supporting key declarations appear
>in the OWL "wish list".  Given how fundamental they
>are in real-world modelling, they ought to become
>more than that.
>
>Cheers, Bob

-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
Received on Tuesday, 6 May 2003 22:33:40 GMT

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