- From: Drew McDermott <drew.mcdermott@yale.edu>
- Date: Fri, 26 Apr 2002 12:37:22 -0400 (EDT)
- To: www-rdf-logic@w3.org
[Sandro Hawke] Here's a test case for rdf/daml inclusion: I have two RDF files of instance data using ontology O1. O1 is available on the web at two different addresses, http://www.example.org/O1-a and http://www.example.org/O1-b File a.rdf imports O1-a, file b.rdf imports O1-b, but are otherwise identical. The contents of O1-a and O1-b are identical. Is the meaning of a.rdf and b.rdf supposed to be exactly the same for all systems, ... This question would be better phrased as: "Are all systems supposed to draw exactly the same inferences from a.rdf and b.rdf?" I would tentatively answer Yes. (I'm taking "supposed to draw" to mean "would be justified in drawing"; obviously, some systems will miss valid inferences others will make.) ... or are applications allowed to hard-code "http://www.example.org/O1-a", along with perhaps some human understand gathered from a telephone conversation between the programmer and the ontology creator? My sense is that the string "http://www.example.org/O1-a" really is special and can be hard-coded, along with ontology information which is not machine-readable. This feels more scruffy but more workable. Can you clarify what you mean by "hard-coded"? I'll assume you mean that some symbols in 01-a have procedural attachments that are missing in 01-b. For instance, 01-a might verify (< 3 5) by calling a built-in "<" function, whereas 01-b might have to resort to using Peano arithmetic. Of course, the fact that 01-a and 01-b are indistinguishable means that 01-a also has Peano's axioms, so the call to the "<" function just speeds the inference up. The only way to get a difference between 01-a and 01-b is to give 01-a a procedural attachment that goes beyond what 01-b knows, leaving 01-b stuck when given any query of the form (< numeral numeral). This is a possible scenario, so if it became common practice for different agents to make their own procedural attachments to symbols in various ontologies I would have to withdraw my tentative Yes. But let's get clear on what that would mean. Your phrase "along with ontology information which is not machine-readable" seems to indicate that 01-a does contain some specification that "<" is to be handled in a special way, but that this spec can't be read by all machines. In that case, 01-a and 01-b would no longer be identical. 01-a would have this mysterious black box sitting in it that 01-b doesn't have. In that case machines that can't penetrate the black box should refuse to use 01-a, and my Yes is restored. The only way to get the difference you want is to have the information about 01-a's specialness reside *outside 01-a.* Anyone anywhere can decide that 01-a is special to it in some way just because of its name. But if you're going to allow that, why not have some agents omit all the assertions in 01-a that contain the symbol 'daml'; while others read 01-a backward and 01-b forward. Meanwhile, 01-c, which contains only the assertion <> zen:enlightenment <zen:satori>, is interpreted by some agents as actually containing exactly the assertions of 01-b. So, to agents in on the trick, 01-a and 01-b, which appear to be identical, are really completely different, and 01-b and 01-c, which appear to be different, are identical. Can I have my Yes back? -- Drew
Received on Friday, 26 April 2002 12:37:37 UTC