[sc34wg3] New SAM PSIs

[Lars Marius Garshol]

* Murray Altheim
| 
| First, I don't understand what a "subtype loop" is logically,
| and I can't quite think what it could be, in FOL terms. Steve?

A subtype loop looks as follows in LTM syntax:

  super-sub(a : superclass, b : subclass)
  super-sub(b : superclass, a : subclass)

(Assuming, of course, that 'super-sub', 'superclass', and 'subclass'
have been assigned the correct PSIs.)

| Secondly, pardon my ignorance of the specifics of this document,
| as I've not read it in great detail, nor have I been privy to
| the discussions leading to it, but I did notice that the SAM
| defines a new set of PSIs equivalent to those in XTM 1.0.
| 
| I wonder what utility these perform, since they're identical.

This was the issue psi-topicmaps.org, which we closed in Baltimore.
See <URL: http://www.ontopia.net/omnigator/models/topic_complete.jsp?tm=tm-standards.xtm&id=psi-topicmaps.org >

I admit it is something of a pain to have a double set, but we felt
uneasy about the old PSIs, which do not follow the OASIS PubSubj
guidelines, and which were also not very clearly defined. 

There will be an XTM document you can merge into your topic maps that
will perform the necessary mapping for you, so I think in practice the
impact will be slight.

| This only seems to add confusion and potential ambiguity, in that
| absent a topic map establishing these identities, implementors must
| now check a PSI against two sets now, not one (this would be
| hard-wired into any topic map engine).

Either that, or they may require the new one, forcing users to either
change their topic maps or merge in the mapping topic map.

| We already have two URLs for each (the PSI from the core.xtm topic
| map and the ID link inside XTM spec), so this makes three.

The ID link inside the XTM spec are not official URIs, and I don't
think anyone supports them. Section 2.3.2 of XTM 1.0 implies that it's
the core.xtm URIs that are to be used.
 
| Also, I realize that the W3C has gone to great trouble to confuse
| the world about the syntax of URLs, but absent an HTTP server to
| link the ID (eg., "type" of
| "http://psi.topicmaps.org/sam/1.0/#type") with a default document
| name such as "index.html" (or "index.xtm"), why was the document
| name left off? 

These URIs will be typed in quite often by humans, and it's good to
keep them short. Leaving off the document name also makes us more
flexible with regard to how the page is produced. We can start using
server-side includes (.shtml) or some scripting system without having
to change the URI. So I think this is a feature rather than a bug.

| It would seem it leaves implementors with little ability to even
| guess what is at the other end of that URL. (Yes, I do realize PSIs
| can be considered as opaque strings).

I think they *should* be considered opaque strings, and that
implementors should never try to guess what is on the other side.  In
fact, I think maybe the PubSubj TC should even say this explicitly.
 
| Without wishing to open a heated debate, could someone clarify at
| least the reason for the new PSIs?

I've tried, but I'm not sure if I've succeeded. You are basically
right in what you say, so it's difficult to get very geared up about
your saying it. :)

Anyway, I was aware of what you said, and so slightly uneasy about
this change, but went along with it even so.

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