W3C home > Mailing lists > Public > public-owl-comments@w3.org > January 2009

Problems with sameness and namedness of individuals

From: Jonathan Rees <jar@creativecommons.org>
Date: Mon, 26 Jan 2009 16:51:40 -0500
Message-Id: <B4A467D6-9225-4FCD-95AB-02986594A029@creativecommons.org>
To: public-owl-comments@w3.org

SSFSS 9.5

"The SameIndividual assertion allows one to state that several  
individuals are all equal to each other, while the  
DifferentIndividuals assertion allows for the opposite  that is, to  
state that several individuals are all different from each other."

If you have several individuals, they can't be equal to each other,  
since otherwise you'd only have one individual; and there is no need  
to state that several individuals are different, since otherwise there  
wouldn't be several of them, there would only be one.

I think what you mean to say is that SameIndividual allows one to say  
that several individual *expressions* all refer to the same  
individual, or that several *apparently* different individuals are  
equal, or something like that.

This is a symptom of a confusion throughout between the document  
expressions and what they refer to. A class is not an IRI, and yet you  
say Class := IRI. Now I realize that 'Class' (upper case) is defined  
formally to be a syntactic thing, and is not at all the same as a  
class, so while this is not to my taste (I would have called it a  
'ClassName', paralleling 'ClassExpression') I can't really object to  
it. But the attitude is dangerous. I think I already pointed out a  
problem of this sort in the introduction.

The treatment of "anonymous individuals" is also very confusing. First  
of all, members of the AnonymousIndividual class are not individuals,  
they are syntactic things denoting individuals. Second, in what sense  
are the individuals anonymous? The nodeid sure looks to me as if it is  
a name for the individual, albeit a local one that is not an IRI. You  
could take "name" = "nym" as a term of art meaning "IRI", so that  
nodeids do not qualify as names, but this seems a stretch. Rather than  
define "name" or "anonymous" technically, I think it would be easier  
to just create a new technical term for this syntactic category such  
as 'blank' or 'blank individual name' or 'local name' or 'node id'.

The construction "with anonymous individuals renamed" in section 11 is  
especially disturbing, since it says directly that anonymous  
individuals have names. There is similar usage in 3.4.

5.6

"Individuals represent actual objects from the domain being modeled.  
There are two types of individuals in OWL 2. Named individuals are  
given an explicit name that can be used in any ontology in the import  
closure to refer to the same individual. Anonymous individuals are  
local to the ontology they are contained in."

Because of SameIndividual, a single individual can be both "named" and  
"anonymous". The error here is confusing the individual with the name  
of the individual (the Individual). What you mean to say is that  
individuals can be named (or designated) in either of two ways, using  
an Individual (or I would say IRI or IndividualName) or using a node  
id; or neither, or both. Named vs. anonymous is a partition of the  
syntactic space of Individuals, not of the space of individuals.

Best
Jonathan
Received on Monday, 26 January 2009 21:52:19 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 26 January 2009 21:52:19 GMT