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Re: Comment: Defining N-ary relations, use of cardinality

From: Ivan Herman <ivan@w3.org>
Date: Wed, 11 Aug 2004 09:17:51 +0200
Message-ID: <4119C81F.1040203@w3.org>
To: Natasha Noy <noy@SMI.Stanford.EDU>
Cc: public-swbp-wg@w3.org
Natasha Noy wrote:
>> A small remark: for the diagnosis relation example I would expect to 
>> have a cardinality restriction on the diagnosis_value and the 
>> diagnosis_probability set to one (there must be a diagnosis, after 
>> all...). I do not think that the the fact of defining this as a 
>> functional property covers that (functional means that there must be 
>> at most one value, right?) You use the cardinality restriction in the 
>> 'buyer' relation later. Regardless on how one interprets this very 
>> example, I think the usage of cardinality is very important in n-ary 
>> relations in general, so it might be more 'didactic' to use it imho.
> Yes, you are right. We tried to be reasonably careful about this, but 
> apparently not completely. Indeed, making something a functional 
> property sets the max cardinality to 1, but doesn't require a value. 
> Setting cardinality for diagnosis_value to 1 would make a lot of sense. 
> I am not sure  though if diagnosis_probability should require a value. 
> What if we don't know the probability?

Fair enough (although, personally I would be scared if my doctor could 
not tell me anything on that;-)

>> Also, in this example, I would expect the diagnosis probability 
>> relation to be a datatype property rather than an object property, 
>> with an xml schema datatype of an interval between 0 and 1. After all, 
>> this is what probability is... (at least as an alternative example to 
>> the 'literal' type object property you seem to use right now)
> I think in this example probability really is a qualitative measure, 
> rather than a quantitative  one. I think we talk about someone with high 
> probability of breast cancer, rather than about someone with probability 
> of breast cancer at 0.85 Besides, OWL doesn't have a good way of 
> defining property ranges, and we'll leave that to a different TF note to 
> discuss. It's probably not very relevant for this particular note (We 
> struggled quite a bit to isolate all the related thorny issues)

I agree for this particular note. But it would be nice if the SWBPD 
would come out with a note where datatype properties are used, possibly 
with some restrictions. The specs are pretty scarce on that subject...

>> A slightly different question: I am not sure what a DL reasoner would 
>> do if, say, Diagnosis_relation was also defined to be of a type 
>> rdfs:Statement. It may not add anything to any inference results, but 
>> might have a 'descriptive' value nevertheless. But I am a bit out of 
>> my league to predict the behaviour of a DL reasoner on this...
> It's out of my area of expertise as well, but I don't think making it 
> rdf:statement would change much.
> Natasha


Ivan Herman
W3C Head of Offices
C/o W3C Benelux Office at CWI, Kruislaan 413
1098SJ Amsterdam, The Netherlands
tel: +31-20-5924163; mobile: +31-641044153;
URL: http://www.w3.org/People/all?pictures=yes#ivan

Received on Wednesday, 11 August 2004 07:18:06 UTC

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