- From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
- Date: Thu, 4 Apr 2002 20:17:09 +0100
- To: "Massimo Marchiori" <massimo@w3.org>, "Pat Hayes" <phayes@ai.uwf.edu>
- Cc: <w3c-rdfcore-wg@w3.org>, "Lynn AndreaStein" <las@olin.edu>
From our charter: [[[ The deliverables [...] are ... + update the RDF Model and Syntax Specification (as one, two or more documents) clarifying the model and fixing issues with syntax ]]] Massimo > In fact, I profoundly disagree here. If there's something where > M&S is very > vague is just anonymous nodes. Even, reading the spec carefully, > one will see that, in fact, this vagueness can be somehow justified, > as anonymous nodes are there seen just as accessories, and not as a > fundamental component of M&S: a facility to avoid having to assign > names, but just a facility. The definitive statement in M&S is (para 41) http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-part#41 [[[ The sentence above does not give a name to that resource; it is anonymous, so in the diagram below we represent it with an empty oval ]]] The RDF Core WG is chartered to clarify that statement, and the amount of angst in the RDF community that that statement caused justifies quite some clarifying. "clarifying the model" in our charter primarily reflects the need to clarify whether the anonymous node is blank or labelled. The (normative) diagrams in M&S show pictures of graphs with blank nodes. We have decided that the use of the word Model in M&S for the data model was confusing, and have, fairly systematically, referred to the same concept as graph or (mainly in the primer as data model). We have clarified the second part of the quoted sentence from para 41 (and the picture below) by making it clear that the graph includes nodes that are blank as well as those that are labelled. The first part of the sentence indicates that there is a resource (corresponding to the blank node). We have clarified that by providing the model theory. We have of course provided a much clearer spec than perhaps the charter writers had in mind, but it is merely a clarification. It is not an "RDF Logic" or "RDF Query", contrast it with N3 and see how much more restrained in its goals it is. The model theory is a crucial part of our key chartered task of clarifying and rearticulating. It is not intended as merely a proprosal, but the heart of the work of clarifying the data model, in that it clarifies the most awkward part of the data model the blank node. An existential reading is not the beginnings of a logic but merely an articulation in the clearest possible language (i.e. the language of logic) how the resource referred to by a blank node and the resource referred to by a labelled node may or may not be the same. A second role of the model theory is in support of RDF schema. You will note that so far the only work we have published on schema is in the model theory. "The RDF Core WG is chartered to complete the work on RDF vocabulary description present in the RDF Schema Candidate Recommendation." I personally find that the schema closure rules within the model theory are an extremely clear and precise way of moving the RDF vocabulary description work forward. The ability to clarify these rules further by use of entailment tests both with and without the schema closure rules active is a further advantage provided by the model theory that is clearly within our principle charter objective - clarity. The ability to produce entailment tests which is furnished by the model theory is further within charter considering the explicit deliverable: "publish a set of machine-processable test cases corresponding to technical issues addressed by the WG" Many of the technical issues we have addressed is about what does such and such an RDF graph mean, and the clarity that is gained by converting these issues into entailment tests is highly advantegeous. The model theory holds the work of this wg together. If it is not normative we have not fulfilled our charter of providing clarity. Massimo > Then, we can debate at length on how the > spec should have been clearer on this (and where the architectural > pitfalls are). We can even decide M&S was not smart and that we need to > redefine and introduce first-class anonymous nodes (not a bad > idea), but it > should be clear the distinction on what *we* are saying, and > what's written > in the normative spec (the only normative thing we have so far). You appear to be saying that: M&S is unclear, hence the only clarification of M&S is that it is unclear. (Anything more precise is adding something that wasn't in M&S). Logically this is correct; but it defeats the charter. Given that the WG is chartered to clarify, in those places where M&S is unclear I believe it is our duty within the charter to make the best decision we can to resolve the lack of clarity. Massimo > So, now the higher level of criticism can be better understood. > If MT is just a proposal, fine (even more: good! as, it helps to > provide a possible good starting point for a next RDF Logic/Query wg). > If on the other hand, it aims to define now the normative RDF Logic, > then I think it's truly beyond scope. > Its formal status is unclear now, so better clarify it. > Jeremy
Received on Thursday, 4 April 2002 14:17:20 UTC