Comment: Defining N-ary relations, use of cardinality

Very nice document.

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.

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)

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...


Thanks

Ivan

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Ivan Herman
W3C Head of Offices
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