- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Mon, 10 Dec 2001 17:28:49 -0600
- To: Jeff Heflin <heflin@cse.lehigh.edu>
- Cc: Deborah McGuinness <dlm@ksl.stanford.edu>, ned.smith@intel.com, jeremy_carroll@hp.com, connolly@w3.org, jos.deroo.jd@belgium.agfa.com, herman.ter.horst@philips.com, hendler@cs.umd.edu, www-archive@w3.org
>Pat, > >Sorry for the terse descriptions in the table, I had assumed that people >could match these back to the documents that Deborah and I sent out >earlier. Details on my list can be found at >http://www.cse.lehigh.edu/~heflin/webont/reqs.html while information >about Deborah's can be found in >http://lists.w3.org/Archives/Public/www-archive/2001Dec/0022.html. >Unfortunately the original list was created by Jim from the various use >cases requested as "homework" so I don't think there is a single place >that provides details on all of them. Of course, you may say that some >of what we have is still vague, but that's actually part of our job. OK, fair enough. Sorry if I havn't been keeping up with all the emails; for the first time in my life, I find it is physically impossible to actually read all my emails, even when the spam is filtered out. >That being said, I'm will to clarify a little bit about what I think >some of these mean. I simply see shared meaning as the requirement that >we have shared ontologies, and that different sources can commit to the >same ontology to express that they share definitions for terms. OK, ta. Question for us to consider: does this amount to more than being able to import terms using URIs? If so, how much more? For example, I suggested an 'imports' primitive to the SUO-KIF group, and it became clear in the subsequent discussion that people wanted to be able to distinguish between 'importing' an ontology wholesale (ie to effectively include one set of axioms in another by naming the set, maybe with a URI); 'importing' an ontology as a set of definitions (where the imported terms may be used in the importing ontology but not redefined or restricted in their meanings, in some sense); 'importing' in the sense of extending a namespace but not importing any content; and even some variations on these, eg importing a concept plus its definitions, but re-naming it in the importing ontology. The resulting syntactic complexity needed to distinguish all these cases seemed rather worrying; people felt that the proposal was getting out of hand in the SUO-KIF context; but maybe there is no way to avoid these complexities on the web. >As for >ontology reusue, I simply see this as the ability to have ontologies >reuse or extend other ontologies. I don't quite see how this is distinguished from sharing. Isn't sharing an ontology simply a form of re-use? >As for ontology evolution, I see this >as dealing more with changing an ontology. For example, if the old >ontology said that "A whale is a fish" then we might want to change the >ontology to fix our mistake. I see this requirement driving the need for >distinguishing between different versions of ontologies and for data >sources to commit to specific versions. OK, ta. But again, the issues seem connected. Eg suppose that the importing/sharing technique allows one to import part of an ontology; then this provides a way to 'change' the ontology - ie create a changed version, in a sense, of the ontology - by importing part of it and adding this to a different extension. There is a completely different set of issues connected with the regrettable fact that URLs are labile, and the same URL might identify a different ontology today from the one it identified yesterday. That is where 'versioning' seems to come in, if I understand that term in a database sense. And that, again, seems to be connected with issues in the logical structure of the language, eg should it be rigorously monotonic? (Yes, BTW :-) >I agree that expressiveness is important, but wonder if that might be >too vague to be useful. I think it is central in the design of any ontology language. The entire DAML+OIL effort so far has been largely driven by the requirement that the language provide an operational sweet spot on the expressiveness/deductive-tractability tradeoff; hence the central emphasis on description logics as a basic framework. Many of us however have either no particular interest in provable deductive tractability, or are willing to risk deductive incompleteness in return for expressiveness and a more elegant proof theory. Should WebOnt continue along these lines, or should we choose a different position on this spectrum? BTW, heres another topic that seems to cut across everything else and seems central, though it's not a use requirement exactly: to get a proper, adequate, semantics for URIs. Right now we treat URIs as though they were simple logical names, but they obviously are not simple logical names, in general. URLs (or the corresponding fragments of URIs) are more like file names, for example. I think that creating a proper semantics for URIs is actually a very tricky problem that might have many repercussions on other topics on the list, eg it would have to come to terms with following enigmatic sentence from RFC 2396, which practically has 'versioning' branded on its forehead: "The resource is the conceptual mapping to an entity or set of entities, not necessarily the entity which corresponds to that mapping at any particular instance in time. Thus, a resource can remain constant even when its content---the entities to which it currently corresponds---changes over time, provided that the conceptual mapping is not changed in the process." Pat -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Monday, 10 December 2001 18:29:02 UTC