- From: Bijan Parsia <bparsia@cs.man.ac.uk>
- Date: Thu, 22 May 2008 00:19:26 +0100
- To: "Peter Ansell" <ansell.peter@gmail.com>
- Cc: "Semantic Web" <semantic-web@w3.org>
On May 22, 2008, at 12:04 AM, Peter Ansell wrote: [snip] > I have a feeling I am mixed up with the idea of classes and instances > and their logic representations. Some of what you say doesn't make > sense to me, but you are very sure about it so I probably should do > some more reading. I get hung up on the idea that you even need to > define a special class for something which can never have any > instances. I can give you a reason why you want to have a special name for it: It's very handy for indicating unsatisfiable classes ina UI. > Am I wrong in saying that you start off with nothing, and them > immediately use that to define everything, and then have subsets of > everything, except for in a case where the subset would be nothing and > it would then be sectioned off into its own world? I would say that you are wrong. That's certainly not how logics are developed. Typically you start off with a definition of the logical connectives (e.g., negation, the quantifiers, etc.). > It just doesn't > seem meaningful, even though it may be proved consistent once I > understand classes and individuals and instances etc. I hope so. I think you need to let go of this line. Try starting with a text on propositional logic. The key bits to look at are tautologies (i.e., theorems) and contradictions. Cheers, Bijan.
Received on Wednesday, 21 May 2008 23:20:10 UTC