[sc34wg3] New SAM PSIs

[Lars Marius Garshol]

* Murray Altheim
| 
| I think you're now missing my point: the "superclass-subclass loop"
| is simply wrong.

We've known each other for long enough now that you should have
learned that arguments are the only things that work with me. I don't
listen to assertions unsupported by argument. (Whether you care about
that is another matter, of course.)

| The whole idea only makes sense in terms of "superset-subset loop."

In one sense that's what it is. Superclass/subclass is, in the strict
logical sense, only a statement about the extensions of the classes,
which are of course sets.

* Lars Marius Garshol
|
| In other words, we don't know that the classes are the same, but we
| do know that their extensions are the same. That's a kind of
| equivalence, and DAML+OIL and OWL *explicitly* allow this in order
| to allow people to express this relationship between classes.
 
* Murray Altheim
|
| You were fine until you said "that's a kind of equivalence." 

Hmmm. I'm surprised. It means the classes are equivalent in terms of
their extensions, right?

| If that's as far as OWL went, fine. But in reading the OWL spec and
| the W3C list archives this goes beyond simply saying they have the
| same extensions; it is making a statement about the classes based on
| the equivalence of extensions, which is where the problem lies. 

Actually, I don't see where that statement is made. Do you have a
reference? (Well, it may be said in a posting to a mailing list, but I
wouldn't necessarily lend much weight to that.)

| I don't know if you remember me mentioning that this was being
| justified on their list via things like RDF and Java's handling of
| classes, which is a different domain entirely (eg., subclassing in
| Java is different than set theory's definitions).

Yeah, I've seen some people drawing this into the discussion, but I
think most of them were just pointing out that the difference might
confuse Java developers. Personally I think that's a non-problem.
 
| If I'm misinterpreting the OWL spec, imagine how many others will do
| so. *sigh*

Well, they do have a model theory that spells this out in excruciating
logical detail. For someone well versed in logic it's kind of hard to
get confused.

<URL: http://www.w3.org/TR/owl-semantics/direct.html#rdfs_subClassOf_semantics >

| Well, we've had a difficulty in communicating a difficult bunch of
| concepts over email. Not always the most efficient means of doing
| this obviously. I'm glad that even though we both seem to get
| frustrated with each other we keep trying... :-)

Agreed. :-)

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no >