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Re: [ontolog-forum] Interpreting OWL

To: ontolog-forum@xxxxxxxxxxxxxxxx
From: "John F. Sowa" <sowa@xxxxxxxxxxx>
Date: Sun, 17 Oct 2010 21:41:06 -0400
Message-id: <4CBBA5B2.3070405@xxxxxxxxxxx>
On 10/17/2010 5:29 PM, Pavithra wrote:
> What is the need to support acyclic structure vs cyclic ?    (01)

Any collection of relations among a discrete set of entities
can be represented by a labeled directed graph -- or by a
collection of tables, as in an RDB.  (If there are infinitely
many entities, the graphs and tables may have to be infinite.)    (02)

For some applications, those graphs (or tables) don't have
cycles.  But most applications (even for something as simple
as a benzene molecule) require graphs that have cycles.
To guarantee decidability of their inferencing methods, OWL
imposes constraints that make it impossible to say or imply
that the structure has cycles.    (03)

For some applications, it's possible to live with that restriction.
But for most applications, it's necessary to have a more general
knowledge representation language than OWL.    (04)

On 10/17/2010 6:21 PM, Rich Cooper wrote:
> But wouldn’t that hierarchy [of professors & grad students]
> be a lattice instead of a tree?    (05)

That depends on what relation between prof & students you intend
to represent.  The relation (X took a course from Y) could have
cycles.  But the relation (X earned a PhD with Y as thesis advisor)
would be a tree, except in rather unusual circumstances.    (06)

John    (07)

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