- From: John F. Sowa <sowa@bestweb.net>
- Date: Tue, 31 Jul 2007 16:52:16 -0400
- To: Sandro Hawke <sandro@w3.org>
- CC: Valentin Zacharias <Zacharias@fzi.de>, phayes@ihmc.us, ivan@w3.org, juanfederico@gmail.com, semantic-web@w3.org
Sandro, I have no objection to that statement (assuming that we can agree on what the term "same semantics" means): > RIF is not a rule language; it a family of related rule languages. > We're calling each RIF language a RIF "dialect". Our plan is to > encourage the dialects to use the same syntax when the semantics > line up, and to require the same semantics whenever the same syntax > is actually used. The ISO standard for Common Logic specifies a very general model theory and an abstract syntax. We also use the term "dialect", but for any syntax that has a semantics-preserving mapping to the abstract syntax. The standard includes three annexes for three dialects that express the full semantics: CLIF, CGIF, and XCL. But any other language that expresses any subset of the semantics can be considered a CL dialect. RDF and OWL, for example, satisfy the requirements to be CL dialects. > ... but formally the semantics are to be specified at the > dialect level. That is very dangerous, because then you must provide a formal proof that two independently specified semantics are logically equivalent. In the worst case, that proof could be undecidable. What we did for CL is to specify the model theory in terms of the abstract syntax. Then that semantics is inherited by the dialects by mapping their syntax to the abstract syntax. This is a much simpler approach, in which any discrepancies between dialects are resolved just by seeing how they are mapped to the abstract syntax. > The idea is that when you're designing a dialect, you should > specify the semantics using Model Theory. If you can't do that, > then you should use Proof Theory. If you still can't then you > may fall back to an operational definition. This is necessary, > as far as we can tell, because we don't have Model-Theoretic or > Proof-Theoretic approach to defined the semantics of the Production > Rule systems which dominate the Business Rules market. That is totally unacceptable. The size of their market is irrelevant. If they can't define their semantics, they've got to be deprecated until they get their acts in gear. There are many standards projects that died because loosey-goosey semantics caused seemingly compliant implementations to be incompatible. When that happens, the market share for the standard quickly becomes ZERO. > The RIF Working Group had a broad mission to cover both logical > rule languages and non-logical rule languages (like the Business > Rules systems mentioned above). The solution is simple. You define the semantics formally. And say that any system supported to the extent that they comply with the definition. Everything else is deprecated. > If we consider the "RIF" box in the layer cake to be "RIF BLD" > then I think we're in good shape with the Unifying Logic. If we > do this, the concerns raised above -- the loophole, etc -- don't > come into play. Fine. Then put RIF BLD into the Semantic Web layer cake, and cast the deprecated versions into outer darkness, where there is weeping and gnashing of teeth. John
Received on Tuesday, 31 July 2007 20:52:35 UTC