[Crm-sig] Implementation recommendation for disjointness

Martin Scholz martin.scholz at informatik.uni-erlangen.de
Tue Nov 22 12:38:46 EET 2011

Dear all,

while working on the Erlangen CRM (<http://erlangen-crm.org>), we came across 
the problem of how to deal with disjoint classes. OWL DL offers the possibility 
to mark two classes as disjoint. We would like to effectively use it. Are there 
any recommendations for the implementation of disjoints, like there are for 
property quantifiers and primitive values?

Unfortunately, the CRM is quite unclear about which classes should be considered 
disjoint: In the current version of the standard there is a section about 
"Disjointness" (page xvi) saying that
"Classes are disjoint if they share no common instances in any possible world. 
There are many examples of disjoint classes in the CRM.
A comprehensive declaration of all possible disjoint class combinations afforded 
by the CRM has not been provided here; it would be of questionable practical 
utility, and may easily become inconsistent with the goal of providing a concise 
definition. ..."
Afterwards, only two disjoints are explained:
E2 Temporal Entity & E77 Persistent Item
E18 Physical Thing & E28 Conceptual Object
Whereas the scope of E2 also directly mentions the disjointness with E77, this 
is not the case for E18 & E28, nor for any other class.

An (out-dated) list of possible disjoint classes is mentioned in issue 92 
(<http://www.cidoc-crm.org/issues.php?id=92>). But the current proposal section 
of the issue also states that a comprehensive list should not be supplied and that
"we should abandon the idea of disjoint class declararations altogether".
Nonetheless, scope note proposals are given for E2, E77, E18, and E28 which 
confirm both aforementioned disjoints (also E18 and E28!).

How should disjointness be dealt with? Is it merely informative and should be 
omitted by implementations, just like the property quantifiers? This would mean 
an enormous loss of expressiveness.
Are there essential disjoints like E2 and E77 that have to be implemented, while 
others are "optional"? Why then among the 5 "second level" classes E2, E52, E53, 
E54, and E77 only E2 and E77 are disjoint?

Martin Scholz

Martin Scholz, Diplom-Informatiker
Friedrich-Alexander-Universität Erlangen-Nürnberg
Department Informatik 8
Haberstr. 2
91058 Erlangen
Tel: +49 9131 852-8984
Fax: +49 9131 852-8986
Mail: martin.scholz at cs.fau.de

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