W3C home > Mailing lists > Public > public-owl-dev@w3.org > April to June 2012

Re: Describing Trees in OWL?

From: Stephan Opfer <stephan.opfer@gmx.net>
Date: Thu, 31 May 2012 19:44:58 +0200
Message-ID: <4FC7AE1A.7050708@gmx.net>
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 GMT

This archive was generated by hypermail 2.3.1 : Wednesday, 27 March 2013 09:32:59 GMT