[sc34wg3] Draft Reference Model

Sam Hunting sc34wg3@isotopicmaps.org
Fri, 22 Nov 2002 22:44:08 -0500 (EST)

> | We've had numerous discussions about this, and the
> | following viewpoint has (so far, anyway) prevailed
> | consistently:
> |=20
> |   A relationship *type* that has only one possible
> |   membership isn't a type of relationship at all.  In
> |   an instance of such a relationship type, nothing can
> |   have a relationship with anything else, by
> |   definition, so it's not a relationship.
> Huh? Does this mean that the
>   borders-with(norway : neighbour, sweden : neighbour)
> relationship is not a relationship according to the RM? Or do I
> misinterpret you?

I would say -- slightly. The relation you model using the above syntax
would have all its implicit members expressed explicitly in the graph.

> * Bernard Vatant
> |
> | That means role type is mandatory. I'm very happy with that, vs
> | <roleSpec> being optional in XTM 1.0.  OTOH assertion type is still
> | optional ...
> =20
> * Steven R. Newcomb
> |
> | Yes.  The syntax doesn't necessarily have to change, however.  There
> | are several ways to handle this, and we should consider all of them
> | carefully.  For example, the Syntax Processing Model for XTM can
> | supply an "unspecified role type" role type, but this may have
> | undesirable consequences for the merging of assertions.  Not to
> | worry, though; there are other approaches, too.
> Like the approach that we took with the SAM in Montr=E9al, and which
> I've pointed to twice already: generate blank placeholder nodes. This
> avoids the undesirable merging, but even so I'm not sure I am happy
> with it.

What are the subjects of these "blank" placeholder nodes?

Not sure what you mean by "generate". Would the Syntax Processing Model
define them?=20

This proposal seems similar to the approach I showed at Montral and
documented at http://www.etopicality.com/RM/WF.shtml -- where I had
"placeholders" (if you mean what I think you mean by that word) for

> | Here's the rationale (at least as I see it):
> |=20
> | (1) In the graph, all role types are mandatory because
> |     without them, there's literally no way to tell
> |     which role player is playing which role.
> Agreed, and this one on its own clinches it for me. Without roletypes
> you have a meaningless assertion.


> | The SAM is free to establish one or more assertion types that
> | determine the subjects of assertion types.  The SAM is also free
> | *not* to do that, and instead to provide its own limited set of
> | built-in assertion types.  If the SAM allows topic map authors to
> | create association types, however, as the HyQ and XTM syntaxes do,=20
> | [...]
> The SAM has no choice, actually. It has to be at least as expressive
> as HyTM and XTM are, otherwise it can't do what it was created to do.
> (HyQ is a typo for HyTM, I presume?)

No. HyQ "is a data content notation for use with HyTime location
addressing facilities" (ISO 10744 first edition). More than that I can't

> | I think the SAM probably must define some assertion/association
> | types that allow the subjects of assertion types to be determined by
> | means of them.  One such association/assertion type could be the one
> | that you're mentioning:
> | "assertionPattern-role-rolePlayerConstraints".
> =20
> This I couldn't follow, but it sounds like a new issue. Could you
> explain what this is?
> | (In the XTM syntax, all this is certainly well-hidden.  And that's
> | probably why the XTM syntax is so intuitive for so many people!)
> | Under the draft RM4TM, the Syntax Processing Model defined by the
> | SAM for XTM must specify how to make what was only implicit in the
> | XTM instance, such as groups that play roles collectively, explicit
> | in the graph.
> Yes. Probably some bits of this will go into the XTM -> SAM spec,
> while others will go into the SAM -> RM spec. The trick will be to
> figure out where to draw the line

Indeed. Clause 5 should help.

Sam Hunting
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