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Re: About self-referential syntactic constructs

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sat, 29 Mar 2003 09:45:48 -0500 (EST)
Message-Id: <20030329.094548.125115541.pfps@research.bell-labs.com>
To: yzqu@seu.edu.cn
Cc: www-rdf-logic@w3.org

From: "Yuzhong Qu" <yzqu@seu.edu.cn>
Subject: About self-referential syntactic constructs
Date: Sat, 29 Mar 2003 10:43:56 +0800

> In Web Ontology Language (OWL) Abstract Syntax and Semantics 
> [2. Abstract Syntax
> ...
> The abstract syntax here is less general than the exchange syntax for
> OWL. In particular, it does not permit the construction of self-referential
> syntactic constructs. It is also intended for use in cases where classes,
> properties, and individuals form disjoint collections. These are roughly
> the limitations required to make reasoning in OWL be decidable, and thus
> this abstract syntax should be thought of a syntax for OWL DL.
> ...
> ]
> What are self-referential syntactic constructs?
> Does it mean the following situation?
> If an axiom uses a class or property to (partially) define itself, then
> this axiom is using a self-referential syntactic construct.

No, this is allowed.

> How about the following situation?
> An axiom uses a class or property (say B) to (partially) define another
> class or property (say A), and the another axiom uses A to (partially)
> define B.

This is also allowed.

> May I use "cross-referential syntactic constructs" to mean the above
> situation?

I haven't heard this term before.

> Further more, what's the constraint on OWL Lite/DL about this issue? How
> does the Description Logic deal with this issue (self-reference/cross
> reference)?

Some early description logic systems (like CLASSIC) did not allow this sort
of thing.  Modern description logic systems (like FaCT and RACER) do.

What is not allowed in OWL is something like

     _:x owl:onProperty ex:p .
     _:x owl:allValuesFrom _:x .

i.e., a description that refers to itself.

> Best regards,
> Yuhzong Qu

Received on Saturday, 29 March 2003 09:46:03 UTC

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