- From: Stephan Opfer <stephan.opfer@gmx.net>
- Date: Thu, 31 May 2012 19:44:58 +0200
- To: public-owl-dev@w3.org
Hi Uli, so cycles are not forbidden, right? Best Regards, Stephan On 05/31/2012 04:10 PM, Uli Sattler wrote: > Hi Stephan, I think we can get a rather good approximation of a tree by > saying the following: > > hasChild is a subproperty of hasOffSpring > > hasOffSpring is transitive > > every offSpring of the root node (i.e., an indiviual called root) has > at most one incoming hasChild edge > (you can also say this for everything in the universe - but that would > be a bit strong) > > if a node has no incoming hasChild edge, then it is the root node > > ...now, if you want a (strict) binary tree you need to add further > cardinality restrictions on outgoing hasChild edges. > > Cheers, Uli > > On 31 May 2012, at 09:40, Stephan Opfer wrote: > >> Hello, >> >> I recently noticed, that although the model of an owl axiom should have >> tree property, it is not possible to describe a tree data structure in >> OWL. The way I would model it, is to create a class Node and a property >> hasChild and make the hasChild property transitive and irreflexive, >> which is not allowed in OWL-DL, because transitive properties are no >> simple properties. >> >> I searched a bit on w3c websites and their citations and also made >> another post on the protege-owl mailing >> list:protege-ontology-editor-knowledge-acquisition-system.136.n4.nabble.com/Tree-Paradox-of-OWL-td4655163.html >> >> Someone told me, that I should post this question here, too. >> >> You don't have to read the other post. Here is a summary of my >> observations and the resulting question to this mailing list. >> >> On website [0] the restriction about composite object properties are >> described and [1] is cited for given the reason for these restrictions. >> However, [1] states about irreflexivity combined with transitivity: >> >> "For SROIQ and the remaining restrictions to simple roles in concept >> expressions as well as role assertions, it is part of future work to >> determine which of these restrictions to simple roles is strictly >> necessary in order to preserve decidability or practicability. This >> restriction, however, allows a rather smooth integration of the new >> constructs into existing algorithms." >> >> So my question is: Has someone proven, that the restrictions about >> transitivity and irreflexivity can be loosen? Otherwise, OWL cannot >> describe a tree data structure on "schema level". >> >> Best Regards, >> Stephan >> >> [0] >> http://www.w3.org/TR/owl2-syntax/#The_Restrictions_on_the_Axiom_Closure >> >> [1] http://www.cs.man.ac.uk/~sattler/publications/sroiq-TR.pdf >> >> > > >
Received on Thursday, 31 May 2012 17:45:34 UTC