Re: [ACTION-78] What it means to define OWL-1.1-Full as a "delta" to OWL-1.0-Full

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Mon, 18 Feb 2008 04:15:14 -0500
Message-Id: <8FAED9B4-E754-497E-BD64-348CF714D30F@gmail.com>
Cc: <public-owl-wg@w3.org>
To: Michael Schneider <schneid@fzi.de>
```
Hi Michael,

This is a nice explanation - I've added it to http://www.w3.org/2007/
OWL/wiki/Different_Kinds_Of_Semantics

I'll make a minor comment - the language of if/then rules and firing,
evokes the idea that the semantic conditions can be implemented by a
rule engine - but the conditions, such as "ICEXT(x), is a subset of
ICEXT(y)" are not the usual sorts of consequents one sees in such
systems - so the analogy might confusing a bit, in addition to the
benefit it brings in helping explain how the conditions work.

Regards,
Alan

On Feb 12, 2008, at 10:12 AM, Michael Schneider wrote:
> == 4. An example of a semantic condition ==
>
> Here is an example for how the layered approach works. The
> semantics for
> subclassing axioms in RDFS and OWL-Full is discussed by looking at the
> respective semantic conditions involved. The following semantic
> condition is
> given in the RDFS semantics spec [4]:
>
>   (SC-SUBCLASS)
>
>   IF
>       <x,y> is in IEXT(I(rdfs:subClassOf))
>   THEN
>       x and y are in IC
>     AND
>       ICEXT(x) is a subset of ICEXT(y)
>
> This semantic condition has the form of a rule. It "fires" its
> "THEN" part,
> whenever there is some triple of the form "x rdfs:subClassOf y" in the
> regarded RDF graph, or when such a triple can be entailed by
> applying other
> semantic conditions from RDFS semantics.
>
> Actually, the "IF" part specifies a slightly different (and more
> complicated
> looking) condition: It demands that the tuple <x,y>, consisting of
> resources
> x and y, is contained in the "property extention" IEXT(.) of the
> property
> denoted by 'rdfs:subClassOf'. This is in fact a statement about the
> interpreted domain, not about the RDF graph itself (remember that RDFS
> semantics is a model theoretic semantics!). But this doesn't matter
> here
> much, since it is essentially what the existence of a triple "x
> rdfs:subClassOf y" means.
>
> Now if this semantic condition fires, we get some new information:
>
>   (1) The not further specified resources x and y are determined to
> be in
> fact /class/ resources. This is expressed by "x in IC", where "IC"
> is that
> part of the RDFS universe, which contains exactly all class
> resources. A
> class resource x is a resource, which additionally owns a "class
> extention",
> i.e. the set of all resources z with "z rdf:type x".
>
>   (2) The class extention of x, named "ICEXT(x)", is a subset of
> ICEXT(y),
> which is the class extention of y. This is, of course, what one
> actually
> intends to express by specifying a subclass axiom.
>
```
Received on Monday, 18 February 2008 09:15:30 UTC

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