- From: Uli Sattler <sattler@cs.man.ac.uk>
- Date: Thu, 31 May 2012 22:28:32 +0100
- To: Stephan Opfer <stephan.opfer@gmx.net>
- Cc: "public-owl-dev@w3.org" <public-owl-dev@w3.org>
Try to build a cycle here... Cheers, Uli On 31 May 2012, at 18:44, Stephan Opfer <stephan.opfer@gmx.net> wrote: > 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 21:40:06 UTC