[tdwg-content] Heretics and illuminati, oh my! [SEC=UNCLASSIFIED]

Paul Murray pmurray at anbg.gov.au
Mon May 9 08:09:31 CEST 2011

On 09/05/2011, at 2:07 PM, Kevin Richards wrote:

> Paul
> I had the same thought (ie the x is of type dwc:Taxon, y is of type tc:Taxon, we know dwc:Taxon and tc:Taxon are equivalent, so we can reasonably compare x and y).
> And this is built into standard semantic web reasoners - which is a bonus.
> But this was debated (taking into account Bob Morris' issue) with respect to DwC and it was decided the benefits weren't significantly better than having a "dwc:isInCategory" sort of property that could then be "equivalent to" another class property and therefore giving you a similar advantage (admittedly not as good, but similar).
> Do you think this is reasonable or are we just losing too much semantic web benefits by not specifying the domain constraint?

A thing to watch out for is that in OWL DL, you cannot apply ordinary data and object properties to vocabulary objects (classes, predicates) - you can only apply annotation properties. If you apply an ordinary data property to a class, OWL DL treats this as what it calls "punning": it decides that there is a class named X and also a named individual named X, and that these have nothing to do with one another. The individual has properties, the class has members, and the annotation properties, well: whatever. Reasoners do not reason over annotation properties: indeed - that's the entire point. Attempting to put properties on properties and having classes being instances of classes results in things that are mathematically undecidable ("this statement cannot be proven to be true").

(another reason is that is allows you to put dc:comments and labels on classes, and even if you declare those classes to be equivalent nevertheless the comment only applies to the particular thing you put it on)

This all means that dwc:isInCategory, if you want to apply it to dwc:taxon or other classes, will never have any meaning that semweb "engines" can get at. The underlying thing is that dwc:isInCategory is actually a meta-syntactic construct: rather than using owl to define a vocabulary, you are effectively attempting to extend OWL itself.

But ... maybe that's ok. Maybe what is attempting to be done here only ever needs to be understood by humans.

Now ... if what you are trying to do is to define "Fish" as an owl class as well as as a Taxon object - that is do-able, even to the point of being able to get inheritance working, using reflexive properties.  At least ... I think it is. I should write a test case.
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