From: pat hayes <phayes@ihmc.us>

Date: Thu, 4 Dec 2003 11:03:19 -0600

Message-Id: <p06001f2dbbf5167f8206@[10.1.31.1]>

To: "lsp" <lsp@is.pku.edu.cn>

Cc: www-rdf-comments@w3.org

Date: Thu, 4 Dec 2003 11:03:19 -0600

Message-Id: <p06001f2dbbf5167f8206@[10.1.31.1]>

To: "lsp" <lsp@is.pku.edu.cn>

Cc: www-rdf-comments@w3.org

>Hi, > >I have some comments about rdfs:subPropertyOf: >1) if (R rdfs:subPropertyOf S) > (R rdfs:domain C1) (R rdf:range D1) > (S rdfs:domain C2) (S rdf:range D2) > can we infer that (C1 rdfs:subClassOf C2) && (D1 rdfs:subClassOf D2)? > >I believe the result can be easily inferred by the RDF Model Theory, >but there is no rule in the RDFS closure rules >to show this inference. Peter Patel-Schneider has pointed out to me that my previous reply may have been misleading, in that in this case it is not in fact even valid to infer that C1 is a subset of C2 (and similarly for the range). The reason is that the domain and range assertions only provide an upper bound on the 'true' domain and ranges, ie the sets of things to which the property actually apply. Thus for example it would be fine to say that ex:parentOf rdfs:domain ex:human . ex:parentOf rdfs:range ex:human . but this does not entail that all human beings have children, only that all parents (and children) are human. The 'real' domain, in the mathematical sense, of this property is the subset of humans who happen to have children, but there need be no RDFS class corresponding exactly to this set (and indeed there is no way in RDFS to specify such an 'exactly-fitting' class by if-and-only-if conditions; there is, however, in OWL.) Thus, the fact that x R y entails x S y and hence that x type C2 (and y type D2) does not itself mean that C1 is a subset of C2; only that the subset of C1 which contains the actual entities to which R applies is a subset of C2: but since this may well be a proper subset of C1, no subset relationship can be inferred between C1 and C2. Sorry if my earlier message was misleading. Pat Hayes -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayesReceived on Thursday, 4 December 2003 12:06:26 GMT

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