From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>

Date: Mon, 29 Sep 2003 09:48:41 -0400 (EDT)

Message-Id: <20030929.094841.63130543.pfps@research.bell-labs.com>

To: www-rdf-comments@w3.org

Date: Mon, 29 Sep 2003 09:48:41 -0400 (EDT)

Message-Id: <20030929.094841.63130543.pfps@research.bell-labs.com>

To: www-rdf-comments@w3.org

Comments on RDF Semantics (version dated 26 September 2003) I did a quick read of the most of RDF Semantics, along with a careful investigation of a couple pieces. Here are my comments. 1/ The major new issue I have with the document is the unsupported change of the entailment rules from informative to normative. 2/ The removal of the translation to LBase is a major improvement. I would have prefered different wording in Section 0.1 concerning this translation but can live with the new situation. 3/ The document is of several minds with respect to just what the semantics of RDF (and RDFS) is. There is wording in Section 1.3 to the effect that the definition of the semantics of RDF and RDFS excludes the entailment rules. How can this coexist with having the entailment rules be normative? 4/ The figures in the copy of the document that I reviewed have naming problems, but I am told that these have since been fixed. 5/ The Monotonicity and Compactness Lemmas are only stated for simple entailment. However, readers could easily be left with the impression that the other forms of entailment could also have the desirable properties that accrue from these lemmas. 6/ The characterization of simple entailment rules is misleading as they do not currently correspond to the instance lemma. The comment on how to make this change at the end of Section 7.1 does not adequately serve to correct the misimpression. 7/ The document needs a better description of consistency and inconsistency. 8/ The change to the RDFS entailment lemma is incorrectly noted in the change log as editorial. 9/ I view the development and statement of the entailment lemmas as fundamentally flawed. I look for soundness and completeness in any such syntactic characterization of entailment. Neither simple entailment, RDF entailment, nor RDFS entailment have both these characteristics. 9a/ Section 7.1 does not provide any statement at all on whether the simple entailment rules are complete with respect to simple entailment. There is a statement that the rules are sound, and that an agumentation of them correspond to the instance lemma, but no proof is presented. SUGGESTION: I suggest that Section 7.1 be augmented with the following Lemma and that its proof be added to Appendix A. Simple entailment lemma. S simple-entails E iff there is a graph that can be derived from S by the application of the simple entailment rules that is a supergraph of E. (Proof in Appendix A.) This lemma requires that the simple entailment rules be augmented to allow vvv in rule se1 and bbb in rule se2 to be a blank node. 9b/ Section 7.2 does not provide an adequate syntactic characterization of RDF entailment. SUGGESTION: I suggest that Section 7.2 be augmented by the following change to the RDF entailment lemma and that its proof in Appendix A be modified accordingly. RDF entailment lemma. S rdf-entails E if and only if ... and which is a supergraph of E. (Proof in Appendix A.) 9c/ Section 7.3 does not provide an adequate syntactic characterization of RDF entailment. SUGGESTION: I suggest that Section 7.3 be augmented by adding the following lemma and providing a proof for it in Appendix A. RDFS consistency lemma. S is rdfs-consistent if and only if it is not possible to derive a supergraph of a graph of the following form from S plus the RDF and RDFS axiomatic triples by the application of the simple, RDF, and RDFS entailment rules uuu vvv rrr^^rdfs:XMLLiteral . vvv rdfs:range www . www rdfs:subClassOf rdfs:Literal . where rrr is a non-well formed XML literal. (Proof in Appendix A.) I believe that this is a correct characterization of RDFS consistency but this would have to be shown in the proof. SUGGESTION: I suggest that Section 7.3 be augmented by the following change to the RDFS entailment lemma and that its proof in Appendix A be modified accordingly. RDFS entailment lemma. If S is rdfs-consistent then S rdfs-entails E if and only if ... and which is a supergraph of E. (Proof in Appendix A.) Peter F. Patel-SchneiderReceived on Monday, 29 September 2003 09:49:27 UTC

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