W3C home > Mailing lists > Public > public-semweb-lifesci@w3.org > May 2007

Re: Advancing translational research with the Semantic Web

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 21 May 2007 11:24:09 -0700
Message-Id: <p06230940c27790b26982@[192.168.1.4]>
To: Phillip Lord <phillip.lord@newcastle.ac.uk>
Cc: public-semweb-lifesci@w3.org

>  >>>>> "CM" == Chris Mungall <cjm@fruitfly.org> writes:
>
>
>   >> Out of curiosity, can you describe how different or similar this
>   >> is to the result that you can achieve in the N-ary relation
>   >> design pattern for OWL?
>   >>
>   >> Obviously, building things into the DL is nice, but it's not
>   >> currently representable in OWL, so would require tooling support,
>   >> while the OWL N-ary relation pattern doesn't.
>
>   CM> I'm afraid I'm unclear how to state the OWL n-ary relation
>   CM> pattern (http://www.w3.org/TR/swbp-n-aryRelations) where I
>   CM> really need it. In all the examples given, the "lifted"[*] n-ary
>   CM> relation was never truly a relation in the first place and
>   CM> always better modeled as a class. It's kind of cheating.
>
>Well, it is kind of cheating, yes, although if it works...

No, really, its not cheating. This reduction of n-ary relations to 
binary+unary relations is quite general and quite sound, and has been 
known and thoroughly understood for over a century. It can always be 
done, and it often makes perfectly good intuitive sense. The 'thing' 
that the arguments all relate to is something like the event, or 
fact, or situation, or state of affairs that holds, etc.. (choose 
your favorite terminology)

>
>   CM> What if my n-ary relation is transitive or if the 3rd argument
>   CM> is a temporal interval over which the relation holds?
>
>The former is hard because it's not clear what do you with n-ary
>relationships. I think that this is true for any
>representation. Fundamentally, if you say "a is part of b" and I say
>"b is part of c", then is "a part of c" and according to whom?

Right, it simply isn't clear what 'transitive' means for relations 
other than binary. Try writing it out as an axiom in logic to see all 
the different possibilities.

>
>It is possible to use build on top of the n-ary relationship, for
>example a symmetric property. Perhaps you could do the same for
>transitivity if you could work out exactly what the semantic should
>be.
>
>
>   CM> I think the former is doable with property role chains. Updating
>   CM> the n-ary relations note with this - and all the other omitted
>   CM> details, such as how to re-represent domain/range, functional
>   CM> properties, n- ary relations in restrictions etc - would take a
>   CM> lot of work and would make it utterly terrifying to the naive
>   CM> user.

Well, naive users probably shouldn't be trying to represent 
functional relations with more than one argument. This kind of thing 
just IS complicated.

My advice to new users is to forget completely about N-ary relations. 
Tell yourself that there are no relations in nature above binary. If 
you think you need one, re-think what you are trying to say so that 
it all fits into the binary case. Chances are this will be fairly 
easy to do, and as a side-effect, you will probably then be much more 
clear on what exactly it is that you want to say about transitivity, 
functionality, domains and so forth.

>Yep, but I think that this reflects the underlying complexities of
>life.

Exactly. Although I would prefer to say, the complexities of awkward 
modes of describing life.

>
>   CM> Nevertheless the results are clunky and will need special tool
>   CM> support [**] to avoid going insane. In general I am wary of
>   CM> design pattern type things - they are usually a sign that the
>   CM> language lacks the constructs required to express things
>   CM> unambiguously and concisely. It sounds like DLR could provide
>   CM> this, which would be great.
>
>Well, this I would agree with. Folding design patterns in, would be
>nice.

Agreed. We made this a central feature of our COE graphic OWL editor, 
in that a user can design a 'template' (a chunk of OWL with gaps in 
it) and give it a name, then just drag-and-drop one into a new OWL 
concept map and fill in the missing parameters. Its a simple device 
and not perfect, but it does seem to be useful.

Pat Hayes
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Received on Monday, 21 May 2007 18:24:21 UTC

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