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

Steve Newcomb srn at coolheads.com
Tue Nov 24 08:30:01 EST 2009

Patrick Durusau wrote:
> Steve,
> Steve Newcomb wrote:
>> 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 tango.
> If you want to *define* the subject "association" to consist of at 
> least two roles, both of which are played but one of the players may 
> be unknown, I suppose.
> What puzzles me is why object to an "unplayed role?"
> Hmmm, ok, say that I play the grandfather role in a grandfather <-> 
> grandchild association. The later role isn't unknown but in fact 
> unplayed, at least at this point in time. ;-)
> Why would you object to my instantiating such an association in my 
> topic map?
Because the subject that is represented by an association (TMDM: by a 
topic that reifies an association) is always a relationship. If fewer 
than two roleplayers are specified (i.e., if fewer than two subjects are 
being said to "be related"), then by definition no relationship is being 
specified. (At least under my own personal understanding of what a 
"relationship" is.)

I've heard some comedian or other say, "I'm married to my imaginary 
lover," while making a crude gesture with one hand. Well, OK, you may 
say that this particular "marriage" is not a marriage, really, but I 
would claim that it is nonetheless a relationship, and that relationship 
is the thing that the crude gesture refers to. Imaginary roleplayers are 
still roleplayers. The subject of a topic can be anything at all, and a 
subject that happens to be a relationship can be any relationship at all.

Actually, though, it's OK with me if a topic map contains an utterance 
of an association with fewer than two specified roleplayers, because it 
might be important to allow interchange of incompletely-specified 
relationships. I'm arguing that, where a Topic Map rhetoric (such as 
TMDM) provides a subject-proxy expression for /relationships /(such as 
association information items)/,/ it be explicit that utterances of 
associations with fewer than two roleplayers are meaningless and should 
therefore be ignored during subject-centric processing. For example, if 
a topic map has two associations, and neither of them has at least two 
roleplayers -- they should not be merged, even if they both have the 
same roles being played (or left unplayed) by the same roleplayer (or 
absence(s) of roleplayers). In Topic Maps, the only reason to merge 
topics is that they are understood (by someone, presumably for some 
reason) to represent the same subject. If a topic has no subject, it 
does not have the same subject as any other topic, even when the other 
topic is subject-less. It has no subject at all, and so it's not really 
a topic at all. Where there is no subject, there is no basis for 
merging, full stop.
> Or is the issue actually what sort of associations are thought to be 
> supported by the TMDM?
I was arguing in the most general way, with respect to subjects that are 
reified (or reifiable) relationships. I think this discussion is 
relevant to TMDM, though, because TMDM provides a special way of 
expressing reifiable relationships, and of reifying them.


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