- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Fri, 28 Sep 2001 10:57:10 -0500
- To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
- Cc: www-rdf-logic@w3.org
...... > > But why bother with all this? The concept of a labelled graph is >> standard and uncontroversial, so this is one place where we can say >> some mathematics in a reasonably intuitive way without sacrificing >> either precision or readability by non-mathematicians. > >I thought that a labeled graph only allows at most one edge between a pair >of nodes, so labeled graphs would not solve this problem. Certainly I've >seen lots of treatments where labeled graphs are defined in this fashion. Hmm, after a quick web check I see that you are right. OK, this point requires another amplification sentence. Thanks for catching this possible misunderstanding. ...... > > >> If we are dealing with untidy graphs, the graph syntax has no >> structural advantages over a lexical syntax, and it would then be >> preferable to simply attach the model theory directly to the >> N-triples notation (which in an earlier version of the model theory >> is what we in fact did, but that had problems of its own.). > >There may be advantages to untidy graphs when looking at complex strategies >for literals. In particular, in the model theory for DAML+OIL, merging >nodes whose labels are literals may change the meaning of the graph. (Of >course the model theory for DAML+OIL doesn't use graphs, but if it did, >such merging would not necessarily be meaning-preserving.) Ah, I had not thought of that in the DAML+OIL context. Can you give a simple example? >[...] >....> >> However, Peter, a question for a professional Description Logician: >> this would allow literals to be assigned non-literal property values >> by an RDF assertion. Wouldn't that break DAML+OIL? > >DAML+OIL depends somewhat on the separation between resources and >literals. Some Description Logics may break severely if their separation >between abstract (resources) and concrete (literals) domains is breached. Right, that is what worries me. I recall this being a sticking point in the DAML discussions for some people, so I presume it is fairly critical there also, no? >[...] > >> >Taking care of rdf:type: >> > >> >A core RDF interpretation, i.e., RDF without reification or containers, is >> >an interpretation over a vocabularly that includes rdf:type with the >> >following extra conditions >> > >> > 1. IS(rdf:type) is in IP >> > 2. IEXT(IS(rdf:type)) <= IR x IR >> >> Is there any real need for condition 2 here in RDF? > >I don't know. The condition is directly stated in M&S. It says that >literals cannot have instances, which is probably a good thing. I'm not sure >what the instance of "2" could be. > >> I hope it can be >> avoided, since it would mean that a triple >> >> aaa rdf:type LLL . >> >> where LLL is a literal, comes close to being a contradiction. Right >> now, all it implies is that IR and LV overlap, but if anyone were to >> ever claim that they didn't overlap, then it would be. I don't like >> having land-mines concealed in the model theory. > >I'm not sure how you get this implication, from your condition 2 on rdf:type, which would be rdf:type rdfs:range rdfs:Resource . in RDFS. > nor am I sure why literals need >to have instances. I tend to agree, but there would be nothing in the syntax to prevent someone writing a triple that says they do, so we would have to give it a meaning. Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Friday, 28 September 2001 11:57:17 UTC