# Re: Detecting cycles in OWL

From: Mikael Pesonen <mikael.pesonen@lingsoft.fi>
Date: Fri, 24 Apr 2020 17:10:52 +0300
Message-ID: <3fa0a768-649b-0deb-a808-27a0ca6e6f00@lingsoft.fi>
```
Thanks Pascal, saves lot's of time if this is not possible by normal OWL
DL means. That PDF looks like worth atleast trying to understand.

Followup question to forum: how does one continue usually when reasoning
capabilities hit the wall? SWRL and SPARQL queries are the next steps?

On 24/04/2020 17.01, Pascal Hitzler wrote:
> You probably find more about these matter than you care about here:
> http://people.cs.ksu.edu/~hitzler/resources/publications/OWL-Rules-2011.pdf
>
> But let me break down your example.
>
> you want to say something like the following:
>
> A(x) AND p1(x,y) AND C(y) AND p2(y,z) AND B(z) AND p4(w,z) AND D(w)
> AND p3(x,w) --> E(x)
>
> And essentially you want to know whether there is anything in the
> class E.
>
> With the rolification technique in the above referenced paper, yo
> would come up with the following to express the axiom:
>
> A equiv exists R_A.Self
> B equiv exist R_B.Self
> C equiv exists R_C.Self
> D equiv exists R_D.Self
> R_A o p1 o R_C o p2 o R_B o p4- o R_D o p3- subPropertyOf R
> exists R.Self subClassOf E
>
> Now, these six axioms *syntactically* translated into first-order
> predicate logic do the trick.
>
> HOWEVER, you would use Self with a non-simple role, which is not
> allowed under OWL DL.
>
> So the short answer is: it doesn't look like it's possible.
>
> The above paper discusses a construct called nominal schemas, which is
> (very complex) syntactic sugar on top of OWL, an which allows you to
> express the rule above, provided that the variable x can bind only to
> individuals actually occurring in the knowledge base.
>
> Best Regards,
>
> Pascal.
>

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