- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Fri, 17 Jan 2003 07:44:46 -0500 (EST)
- To: www-webont-wg@w3.org
Technical Issues to be resolved before last call Here are some issues that I feel must be resolved before OWL goes to last call. I have battled to get the RDF issues resoved, but to little success. I would like to have formal votes on all the proposed resolutions herein. Issues with XML Schema: 1/ The value spaces of xsd:decimal and xsd:float are not disjoint. Right now in both XSD datatyped RDF and OWL the denotation "234.5"^^xsd:float is an element of the class extension of the denotation of xsd:decimal. PROPOSED RESOLUTION: The class extensions of xsd:decimal and xsd:float are not disjoint. The class extension of xsd:float is a subset of the class extension of xsd:double. Issues with RDF Concepts: 1/ The notion of social meaning has no place in the specification of a formal system. PROPOSED RESOLUTION: Social meaning, as defined in the RDF Concepts document, has no effect whatsoever on the meaning of OWL ontologies. NB: I view this as an extremely serious issue. Issues with the RDF model theory: Caveat: The RDF Semantics document may change, and has recently changed. The issues here may be affected by any upcoming change, and have been affected by the recent changes, which I have not completely analyzed. I have not yet received responses to many of my recent comments on the RDF model theory nor have I been given any sort of change list for any of the recent changes to RDF Semantics. The following is only my best guess at the current situation. 1/ The class extension of rdfs:Literal does not necessarily include strings. Right now, "a" rdf:type rdfs:Literal . is not RDFS-entailed by the empty graph. Also, without the following fix, "a" rdfs:type _:x . _:x owl:complementOf rdfs:Literal . is not OWL Full entailed by the empty graph. PROPOSED RESOLUTION: Add to the second table in the OWL model theory if E is then CEXTI(SI(E)) = rdfs:Literal LV As well, add a note to the effect that this is a change to the meaning of rdfs:Literal. NB: This condition *is* already present. However, I feel that the WebOnt working group should explicitly resolve this point. NB: This is a significant extension of the RDFS model theory, with lots of observable consequences. 2/ XSD-interpretations in RDF include the problematic XML Schema datatypes. Current situation: OWL interpretations are defined from D-interpretations where D consists of the appropriate XML Schema datatypes, not from XSD-interpretations. PROPOSED RESOLUTION: OWL interpretations are not defined from XSD-interpretations. 3/ There is no definition of literal strings or language tags in the RDF Schema document. PROPOSED RESOLUTION: Literal strings are Unicode strings. PROPOSED RESOLUTION: Language tags are as in RDF Concepts. 4/ There is contradictory and unclear information with respect to what is a datatype as well as to the treatment of typed literals. Datatypes are sometimes elements of the semantic domain, denoted by URI references, and sometimes the URI references themselves. There is no necessary connection between the intended URI reference for a datatype and the datatype itself. PROPOSED RESOLUTION: A datatype is a formal object, consisting of a URI reference, a lexical space (which is a subset of the Unicode strings), a value space, and a lexical-to-value mapping from the lexical space into (not onto) the value space. In a D-interpretation containing the datatype d = <U,L,V,L2V>, a/ D <= ICEXT(I(rdfs:Datatype)) a/ IS(U) = d; b/ ICEXT(d) = V; c/ for l in L and t a langauge tag, IL("l"^^U) = L2V(l) and IL("l"@t^^U) = L2V(l) d/ for l not in L and t a language tag, IL("l"^^U) is not in LV and IL("l"@t^^U) is not in LV NB: Under this resolution rdf:XMLLiteral is *not* a datatype. NB: Under this resolution I("aa"@en^^xsd:decimal) is not necessarily the same as I("aa"@fr^^xsd:decimal). 5/ The non-normative parts of the RDF model theory, including the closure rules and the translation to Lbase, have many errors. PROPOSED RESOLUTION: The W3C Web Ontology Working Group notes that the RDF Semantics document has numerous errors in its non-normative sections. None of these sections are to be used to provide guidance as to the meaning of RDF or OWL where the normative sections of the RDF Semantics document are unclear, contradictory, or silent. NB: I feel very strongly that WebOnt needs this resolution. There are important places, such as the definition of what is a datatype and the treatment of rdf:XMLLiteral, that are unclear or contradictory in the RDF Semantics document, but where the non-normative sections of the document clearly use only one of the possible interpretations. Peter F. Patel-Schneider Bell Labs Research Lucent Technologies
Received on Friday, 17 January 2003 07:44:56 UTC