Fwd: summary: acyclic class hierarchy

Folks, Frank Harmelen sent me his own perception of the discussion of 
this issue on the DAML telecon this week. I'm forwarding it (with his 
OK) to give a better impression to the WG.

Pat Hayes

>X-Authentication-Warning: mail.daml.org: majordom set sender to 
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>Date: Wed, 29 Aug 2001 00:31:15 +0200
>From: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
>Organization: Vrije Universiteit Amsterdam
>X-Accept-Language: en-US,nl
>To: joint-committee@daml.org
>Subject: summary: acyclic class hierarchy
>Sender: owner-joint-committee@mail.daml.org
>
>
>For what it's worth, here is my summary/understanding of what we 
>could say to the RDF Core group in response to their proposal to 
>enforce acyclicity of subClassOf.
>
>Frank.
>   ----
>
>1. in DAML+OIL, subclass-relations can be inferred even if they are 
>not explicitly stated (note that this is an important difference 
>from RDF-S, where A is only a subclass of B if >*and only if*< there 
>is an explicit statement to that effect).
>
>2. as a result of point 1, acyclicity of the subclass-relation in 
>DAML+OIL cannot always be detected by purely syntactic means, since 
>computationally expensive inference may be needed to detect implicit 
>("implied") subclass-relations
>
>3. because of point 2, DAML+OIL cannot require acyclicity of the 
>subclass-relationship, since that requirement could only be enforced 
>at great computational expense.
>
>4. Point 3 means that if RDF-S will enforce acyclicity of 
>rdfs:subClassOf, then DAML+OIL can no longer use rdfs:subClassOf. In 
>other words, DAML+OIL will be forced to introduce daml:subClassOf
>
>5. Point 4 would mean that much (all?) backward compatability 
>between RDF-S and DAML+OIL would disappear: an RDF-S processor would 
>be unable to catch any of the semantics of a DAML+OIL ontology 
>(whereas currently, all the explicitly stated subclass relationships 
>in a DAML+OIL ontology are accessible to an RDF-S agent, since 
>DAML+OIL uses rdfs:subClassof
>
>6. An important design rationale behind DAML+OIL (and in fact much 
>other stuff on the Semantic Web so far) has been a layered approach, 
>where languages are stacked on top of each other, with as much 
>partial interpretation between the layers as possible. Tim BL has 
>even argued in [1], [2], [3] and many other places that such 
>"partial understanding is an essential design principle of the Web 
>in general, Semantic or not.
>
>The decision to make rdfs:subClassOf acyclic will force DAML+OIL to 
>introduce daml:subClassOf, and will therefore lead to an almost 
>total loss of partial understanding between these two closely 
>related ontology languages...
>
>Frank.
>   ----
>
>[1] Evovability, WWW7 keynote speach, 
>http://www.w3.org/DesignIssues/Evolution.html
>[2] "Web Architecture from 50,000 feet" 
>http://www.w3.org/DesignIssues/Architecture.html
>[3] "Web Architecture: Extensible languages" 
>http://www.w3.org/DesignIssues/Extensible.html

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Received on Wednesday, 29 August 2001 17:48:41 UTC