- From: pat hayes <phayes@ai.uwf.edu>
- Date: Wed, 29 Aug 2001 14:49:48 -0700
- To: w3c-rdfcore-wg@w3.org
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 >owner-joint-committee@mail.daml.org using -f >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 --------------------------------------------------------------------- (650)859 6569 w (650)494 3973 h (until September) phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Wednesday, 29 August 2001 17:48:41 UTC