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RE: RDFTM: RDF reification

From: Steve Pepper <pepper@ontopia.net>
Date: Fri, 24 Mar 2006 12:59:21 +0100
To: "Pat Hayes" <phayes@ihmc.us>
Cc: "SWBPD list" <public-swbp-wg@w3.org>

Hi Pat,

Your intervention in this discussion is much appreciated.

| >[Regarding the issue of whether reification has the same
| >semantics in Topic Maps and RDF]
| Sorry, I have only just seen this thread.

This reply doesn't attempt to answer all your questions: others
are better qualified to do that. But a couple of comments might
help the discussion along.

1. The basic fact that Bill and Sue are married (your #2) can
be represented in TMs as a typed binary association between
what TMs term the two "subjects" Bill and Sue who play the
roles of husband and wife. Thus (in LTM notation, which is
hopefully self-explanatory):

   married-to( bill : husband, sue : wife )

This association can be reified such that the relationship it
represents itself becomes a subject which can play roles in
further relationships:

   married-to( bill : husband, sue : wife )
Thus it is possible (in TMs) to state that (A) Bill and Sue are
married and that (B) their marriage dates from a certain date,
as two separate associations and yet still know that we are
talking about the same "thing" (the relationship, in the common
use sense of the word):

 (A)  married-to( bill : husband, sue : wife )

 (B)  {marriage-of-bill-and-sue, start-date, [[2005-08-20]]}

Note: (B) is here expressed as an occurrence since the date is
represented as a string rather than a topic.

| Then we can distinguish
| 2. The fact that Bill and Sue are married
| 3. The particular state of being married that 
| holds uniquely between Bill and Sue (and no 
| others)

2. As Lars Marius pointed out, it is hard to see the difference
between these two from the Topic Maps point of view. Perhaps
this is precisely because Topic Maps is NOT based on logic, but
rather seeks to model a fuzzier and more natural language
oriented view of the world?


Steve Pepper <pepper@ontopia.net>
Coordinator, W3C RDF/TM Task Force
Received on Friday, 24 March 2006 11:59:30 UTC

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