W3C home > Mailing lists > Public > www-webont-wg@w3.org > June 2003

Re: Proposed Solution: Non-global Keys

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Sat, 21 Jun 2003 15:05:31 +0100
Message-ID: <16116.26155.302661.620640@galahad.cs.man.ac.uk>
To: Dan Connolly <connolly@w3.org>
CC: www-webont-wg@w3.org

Dan,

Further to our teleconf discussion about compound/composite keys, the
paper [1] (which I mentioned in my proposed response to BM) describes
the latest state of research on supporting them in DL reasoning. The
fact that reasoning with such keys is still a topic of current
research seems to be a good justification for not supporting them in
OWL. I'm sure we had this discussion in the WG, but I still can't find
the record.

Ian

[1] http://www.cs.man.ac.uk/~horrocks/Publications/download/2003/LAHS03a.pdf

On June 19, Dan Connolly writes:
> 
> On Mon, 2003-06-16 at 21:12, Jim Hendler wrote:
> > Here is my proposed response on this issue.  I suspect that Dan had
> > something else in mind,
> 
> Yes... what was that... ah, good; the 8 May minutes capture it:
> 
> "Dan - three issues:
>     1 has exactly one - asked and answered,
>     2 Qualified cardinality,
>     3 compound keys not yet covered by an issue"
> 
> My first point was that I thought his hasSSN example
> was something we can currently express, and the only
> difference was syntactic sugar like "hasExactlyOne";
> but I see from Ian's message[2] that this isn't so.
> 
> You've addressed the 2nd point, but I don't
> see anything in your response about compound keys.
> 
> His comment about compound keys...
> 
> > >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.
> 
> is essentially a request to add compound keys to
> our requirements. The closest thing is "complex datatypes";
> quite a stretch... hmm... we called them "records (complex datatypes)"
> in the Jan 2002 ftf.
> 
> The 8 May minutes say "Hard to add compound without adding syntax.  
> Should not come up in next agenda"; I guess I can look at that
> as the chair saying that MacGregor's comment doesn't have
> sufficient new information that we should re-open our decision
> not to have such a requirement. Now... when did we make
> that decision?
> 
> The decision to take requiremnts to last call is sort of
> an implicit decision not to have such a requirement
> http://www.w3.org/2001/sw/WebOnt/ftf5.html#Closure
> 
> In sum, I suppose the rationale for not having compound
> keys is "we can do a bunch of interesting stuff without
> them."
> 
> I think it would be much more responsive if we elaborated
> the stuff in/near "complex datatypes" in the requirements
> document to explicitly discuss modelling records and keys and
> the tradeoffs. Jeff, do you feel inspired to take
> MacGregor's comment and Ian's discussion[2] and add a paragraph
> or two to the requirements document?
> 
> 
> >  but the below seems to address the comment -- If anyone has anything
> > more contentive to add, I'd welcome it
> 
> I'd suggest rather the rationale for postponing QCRs were
> given by copy as well as by reference, but that's not critical.
> 
> 
> 
> >  -JH
> > 
> > --------------
> > 
> > Dear Bob-
> >  Thank you for your comment, the working group has considered it
> > carefully.  We considered how this could be added to OWL - see the
> > discussion thread starting at [1] and particularly [2].  The group
> > considered the addition of Qualified Cardinality Restrictions, which
> > we believe are needed to implement the sort of global keys you need. 
> > However, the WG decided to postpone the issue of QCRs as discussed in
> > my response to Alan Rector at [3].
> > 
> > Please let us know if this decision to (a) acknowledge that our
> > design is lacking, but (b) postpone further design work to a future
> > version is acceptable.
> >    -Jim Hendler
> > 
> > 
> > [1]
> > http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0064.html
> > [2]
> > http://lists.w3.org/Archives/Public/www-webont-wg/2003May/0085.html
> > [3]
> > http://lists.w3.org/Archives/Public/public-webont-comments/2003Jun/0024.html
> > 
> > 
> > 
> > 
> > 
> > >Date: Tue, 06 May 2003 14:22:16 -0700
> > >To: public-webont-comments@w3.org
> > >From: Bob MacGregor <macgregor@ISI.EDU>
> > >Subject: Non-global Keys
> > >X-Archived-At:
> > http://www.w3.org/mid/5.1.1.6.0.20030506142115.00bb75c0@tnt.isi.edu
> > 
> > >
> > >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     *** 240-277-3388 (Cell)
> > http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER
> > ***
> -- 
> Dan Connolly, W3C http://www.w3.org/People/Connolly/
> 
Received on Saturday, 21 June 2003 10:02:23 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:58:01 GMT