Re: [topicmaps-comment] Re: RDF/Topic Maps: late/lazy reification vs.early/preemptive reification

["Steven R. Newcomb" <srn@coolheads.com>]

[Piotr Kaminski:]
> Let me explain with the help of an example. [1]  Suppose we wish to model
> a network of clubs and the membership of each.  The natural representation
> in RDF [2] is to have a number of club and person resources, and attach
> them appropriately with member-property arcs.  In TM, each club and person
> would be a subject, and we'd have one membership association per club,
> with the club playing the "organization" role, and the people playing the
> "member" role (one player per member).
> 
> So far, so good.  However, the clubs are very exclusive, and membership
> needs to be sponsored.  We, of course, wish to record the sponsor(s) of
> each member of each club.  Sponsorship is not a property of the club
> itself, since it has many members each with different sponsors.  It is
> also not a property of the people themselves, since each is a member of
> multiple clubs, probably with different sponsors.
> 
> In RDF, a natural way would be to reify each "member" statement, then
> attach the statement resource to the sponsors with sponsor-property arcs.
> This would unambiguously communicate the sponsors of each person's
> membership in each club.
> 
> In TM, the situation is far trickier.  People play roles in a membership
> association.  We'd now like to make statements about each "playing".
> Unfortunately, TM doesn't preemptively reify this relationship, and does
> not provide us with any special mechanism to do so. [3]

> [3] As far as I know -- my argument rests on this point, so please correct
> it if it's wrong.

Well, at least in my opinion, your example is a compelling
demonstration of a feature of Topic Maps that (a) is not available in
RDF, and (b) answers the problem you raise.  That feature is the fact
that a single TM association can have *any* number of distinct roles,
from 2 to n.  RDF statements are limited to two roles.

A single TM association that fully reifies the concept you describe
might have a "club" role, a "member" role, and a "sponsor of member"
role.  Three roles is no problem for a TM association.

  (BTW, I'm experimenting with calling TM associations "assertions"
  these days when I'm comparing them to RDF "statements", which I'm
  also experimentally calling "assertions".  Using that jargon, here's
  an alternative paraphrase of what I just said:

     "...a single TM assertion can have *any* number of distinct
     roles, from 2 to n.  RDF assertions are limited to two roles.  A
     single TM assertion that fully reifies the relationship you
     describe might have a "club" role, a "member" role, and a
     "sponsor of member" role.  Three roles is no problem for a TM
     assertion."

  What do you think?)

-Steve

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