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

Steve Newcomb srn at coolheads.com
Mon Nov 23 17:02:56 EST 2009

Patrick Durusau wrote:
> Steve,
> Steve Newcomb wrote:
>> 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.
> Moments when an association is only partially expressed?
> Hmmm, ok, what about marriage and one role player known but spouse is 
> not? A partial baptism record for example. Not ever going to cure that 
> lack.
> May not know who the other role player is but the existence of the 
> association is not in doubt.
> A subject is lost by omitting the association. That is "a" choice but 
> it isn't one that should be a rule for all topic maps.
"Unknown role player" is very different from "unplayed role".

I would claim that in the example you provide, the role is not unplayed. 
It is played by an unknown person, at least if the relationship is known 
to exist. I guess if there's a baby to be baptized, that's evidence 
enough that a relationship exists, since human reproduction takes two to 

Well, hmmm, except in cases of parthenogenesis, of course. But in cases 
of parthenogenesis, the father role is unplayed, and therefore it's ok 
for the association to be ignored, because its subject doesn't exist.

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