[sc34wg3] New TMCL slides: at least 2 roles must be played
srn at coolheads.com
Tue Nov 24 08:30:01 EST 2009
Patrick Durusau wrote:
> Steve Newcomb wrote:
>> Patrick Durusau wrote:
>>> 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
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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