[sc34wg3] New TMCL slides: at least 2 roles must be played

Steve Newcomb srn at coolheads.com
Mon Nov 23 13:15:16 EST 2009

Lars Marius Garshol wrote:
> I can see a need for omissible role types in n-ary relationships where 
> it may be the case that one of the role players is not known, but in 
> binary relationship then if one of the players is not known you can 
> simply omit the entire relationship.
I like this rule, but I think it should be more general. Even in an 
n-ary association, if there's only one role player, there's no 
relationship, so the whole association is otiose. The rule should be: 
/At least two roles must be played/.

The only thing that bothers me about this rule is that there may be 
moments when an association is only partially expressed. But I'm not 
sure that it's an issue, really.
> I should add that TMDM didn't define the concept of an association 
> type this way simply because it sounds nice. We really need a common 
> conception of what associations are and how they work. Years ago 
> people were thinking that
> soccer-team(coach: a, player: b, player: c, player: d ...)
> was perfectly acceptable modelling, but today that is thankfully no 
> longer the case.
> As we narrow down the community view of the acceptable uses of 
> associations it becomes easier to write generic reusable software for 
> working with associations that can handle all topic maps.
> In the case of the foo/bar association above, the Omnigator, the 
> Vizigator, and the Ontopia related-topics portlet would all treat 
> those two associations as being effectively the same. (Ontopoly would 
> not let you formulate the rule that the relationship could work this 
> way.) If they really are semantically different that would be bad.
Wow. I'm so surprised that I think I must misunderstand you, or maybe 
I've lost some context here. The two associations:

association-type(role-a: foo, role-b: bar)


association-type(role-a: foo, role-c: bar)

would be regarded as the same, despite the difference in their role 
types? Do you mean that they would merge?

> So, in short, here is a use case that I can see absolutely no 
> practical use for, which complicates TMCL, and which makes it much 
> harder to write Topic Maps software. It might have some nice 
> philosophical properties, but to me personally that does not carry 
> much weight.
I'm lost. What use case? Are you talking about associations in which 
there's only one role player?

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