From: Ginsberg, Allen <AGINSBERG@imc.mitre.org>

Date: Mon, 18 Sep 2006 12:36:41 -0400

Message-ID: <90A462F2D6E869478007CD2F65DE877CF94E71@IMCSRV5.MITRE.ORG>

To: <public-rif-wg@w3.org>

Date: Mon, 18 Sep 2006 12:36:41 -0400

Message-ID: <90A462F2D6E869478007CD2F65DE877CF94E71@IMCSRV5.MITRE.ORG>

To: <public-rif-wg@w3.org>

Hello All, In regard to the action: [NEW] ACTION: aginsber to gather definitions of covers and propose a synthesis [recorded in http://www.w3.org/2006/09/12-rif-minutes.html#action11] Please review the following report. Thanks, Allen. Report on "Covers" Issue 1. Original statement of the issue According to http://www.w3.org/2005/rules/wg/wiki/Design_Constraints/Terminology : "A ruleset is covered by a RIF Dialect if that dialect can be used to faithfully convey that ruleset. (Exactly what it means to "faithfully convey" the ruleset still needs to be refined.) A language is covered by a RIF Dialect if and only if all rulesets which can be written in that language are covered." So here the issue is left in terms of coming up with a definition of "faithfully convey." 2. Subsequent proposal at F2F3 Here are the contents of a slide by Christian: < RIF covers L > means that any expression E1 in L can be mapped into a RIF fragment and back into an expression E2 in L that is equivalent to E1 according to the semantics of L (and thus, may be identical) < RIF covers L1 and L2 > means that, if there is a mapping from L1 to L2 that is semantic preserving in some sense, any expression E1 in L1 can be mapped into a RIF fragment and back into an expression E2 in L2 that is equivalent to E1 in the same sense 3. Discussion of Christian's proposal i) It seems to me that these "definitions" should actually be derivable from a more fundamental defintion of the notion of coverage. ii) The defintions should be stated using the notion of WFFs (well-formed formulas) instead of "expressions" and "fragment." 4. Alternative approach (Model-based approach) Let R be a set of WFFs in some language L. Let M be the set of all models of R (according to the semantics of L). Let R' be a set of WFFs in the RIF (or some dialect thereof). Let M' be the set of all models of R' (according to the semantics of the RIF or the relevant dialect thereof). Then R' "faithfully conveys" R if and only if M = M'. The RIF "covers" L iff for every set of WFFs in L there is a set of WFFs in the RIF that faithfully conveys the former. 5. Discussion of Model-based approach i) It is probably too restrictive. It is probably enough for the two sets of models to be isomorphic. But this is a relatively minor point. ii) It is an "ontological" statement, i.e., it says "what it is" for two sets of WFFs to be related in a certain way. How, in practice, one would prove that the definition holds in a particular case is another matter. iii) Also, even if we know that a language L is covered by the RIF in the model-theory sense, it doesn't follow that there is an algorithm for translating from L to the RIF (and back). That seems to me to be yet another issue. 6. Synthesis There is a difference between saying that the RIF covers a language L in the sense of "faithfully convey," and saying that rulesets in L can be translated into the RIF (and vice versa) algorithmically. Whatever definition of "coverage" (or alternative terminology) we ultimately choose, we need to show that we are aware of this distinction. Perhaps "Coverage" as a goal should be broken into two goals: 1) expressivity (corresponding to model-based notion of coverage) and 2) translatability (corresponding to the operational notion of being able to translate between languages).Received on Monday, 18 September 2006 16:38:41 GMT

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