- From: Ossi Nykänen <onykane@butler.cc.tut.fi>
- Date: Fri, 31 Jan 2003 13:21:35 +0200 (EET)
- To: www-rdf-comments@w3.org
Dear all, I have few remarks concerning the RDF specifications (LCWGs). Outline: #1. RDF-CONSEPTS: The term RDF core is used vaguely (e.g. in sect 1). #2. RDF-CONSEPTS: Example in 3.5 fails to model an actual database? #3. RDF-CONSEPTS: Characterisation on 4.4 about the social meaning of RDF entailments is too strong to be acceptable. #4. RDF-SEMANTICS: A typo in 3.1 in the term rdfV? Here are the full comments: #1.) In document Resource Description Framework (RDF): Concepts and Abstract Syntax (http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/) the introduction uses the term "RDF core" rather vaguely, e.g. by saying that: "The framework is designed so that vocabularies can be layered on top of a core. The RDF core and RDF vocabulary definition (RDF schema) languages [RDF-VOCABULARY] are the first such vocabularies." ... so RDF core is a vocabulary build on top of a core? Perhaps the intended meaning of the concept "RDF core" (the WG, the fundamental set of RDF specs, or something else?) should be spelled out better since the term "RDF core" will be probably widely used in the discussions about RDF hereafter? #2.) In document Resource Description Framework (RDF): Concepts and Abstract Syntax (http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/), the subsection 3.5. "Representation of Simple Facts" provides an example of encoding a database row as a set of RDF statements. The example is nice but perhaps a bit misleading since databases come with the basic assumption of unambiguous data. If I'm not mistaken, the semantics of the RDF core specifications (RDF Schemas in particular) do not provide a validation mechanism preventing the occurrence of multiple values for the cells when the database is modelled as in the example. For instance, someone might simply write two sentences _:x http://.../city "Bedform" _:x http://.../city "Berlin" which effectively would brake the idea of a database. (For predicates this of course is no problem since they are effectively relations.) #3.) In document Resource Description Framework (RDF): Concepts and Abstract Syntax (http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/), the subsection 4.4. "Interaction Between Social and Formal Meaning" (http://www.w3.org/TR/2003/WD-rdf-concepts-20030123/#section-Interaction) reads: "The meaning of an RDF document includes the social meaning, the formal meaning, and the social meaning of the formal entailments. The assertion of an RDF graph G, when G logically entails G', includes the implicit assertion of G'. The implied assertion of G' should be interpreted using the same social conventions that are reasonably used to interpret the assertion of G." This sounds like a rather strong normative characterisation (perhaps too strong). First, even if I believed that (human or artificial) agents would mutually agree a mechanism for making global vocabulary entailments, I don't think that agents in general are capable (or willing!) of stating only RDF sentences whose entailments they fully agree (or can come feasibly up with and interpret). In addition, by introducing a vocabulary entailment including negation, it's easy to end up with unintentional entailments (effective anything). More reasonable would be saying that agents must either agree on the demonstrated entailments, refine their assertions, or choose a different interpretation theory altogether. Second, in practical situations, there are typically several possibilities for the selection of the RDF graph, only some of which an agent is either capable or willing to consider. For instance, I might only have access to graphs G1, G2, and G3, but willing only to accept the assertions in G1 and G3. Thus if G1 asserts {A->B, E->C}, G3 asserts {C->D}, and even if G2 asserts {B->D}, I would accept only {A->B, E-C, C->D} but not {A->C}. However, there might be a graph G4 (that I, e.g., don't know about) which entails {B->E}, using assertions and inference mechanism that I would accept. From mathematical point of view, the result would be the same (accept G2 or not, by accepting G1, G3, and G4 one would entail A->C), but from the metamathematical point of view, quite different (different proof)--I might argue the same thing as the next guy but with different arguments. In the social context this is extremely important (consider, e.g., the system of law). Thus the entailment path itself should be on focus as well as the result. A trivial example to emphasise this point: G1: {A->C} G2: {A->B, B->C} Socially accepting G1 alone might be harder that its "proof", G2 (which logically does entail G1). (Consider: "JohnSmith is a clown" versus "JohnSmith acts foolishly" and "foolishly acting people are clowns" thus "JohnSmith is a clown".) Perhaps RDF should introduce new concepts, for denoting the particular graph an agent is using (capable and willing) while doing deductions and interpretations, and the notion of a proof (i.e., some assertions are "more valuable" than others since there is a widely accepted proof for them)? #4.) In document RDF Semantics (http://www.w3.org/TR/2003/WD-rdf-mt-20030123/), the first paragraph of the subsection reads: "RDF imposes some extra semantic conditions on the following (rather small) vocabulary, which we will call rdfRV:" and goes on introducing the RDF Vocabulary in a table. It seems that the name "rdfRV" is a typo which should be replaces with the name "rdfV"? In general, I very happy to see RDF taking shape, thanks! Best regards, --Ossi -- Ossi Nykänen Tel +358 3 3115 3544 Tampere University of Technology Fax +358 3 3115 3549 DMI / W3C Finnish Office Email ossi@w3.org P.O.Box 553, FIN-33101 Tampere, Finland Web www.w3c.tut.fi
Received on Friday, 31 January 2003 06:21:41 UTC