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Re: RDFTM: RDF reification

From: Lars Marius Garshol <larsga@ontopia.net>
Date: Fri, 24 Mar 2006 10:27:35 +0100
Message-Id: <F2BC5446-7A32-414A-968D-561F38DE2DC2@ontopia.net>
To: SWBPD list <public-swbp-wg@w3.org>

* Pat Hayes
> Sorry, I have only just seen this thread.

It only just started, so no worries.

> RDF reification describes a stating (a particular instance, or  
> token, of a syntactic entity) which is about as far as one can  
> reasonably get from something semantic, which I gather from your  
> emails is what "reification" means in TM.

Yes, this is my understanding, too.

> Suppose the basic fact is that Bill and Sue are married. Then we  
> can distinguish
> 1. Married, which is a binary relation: in RDF/OWL, a property.
> 2. The fact that Bill and Sue are married: in RDF/OWL, represented  
> by a triple.
> 3. The particular state of being married that holds uniquely  
> between Bill and Sue (and no others): what in philosophy is often  
> called a 'trope' (see eg http://en.wikipedia.org/wiki/ 
> Trope#Tropes_in_philosophy). This has no standard RDF  
> representation, but it could be described, somewhat artificially,  
> as a subproperty of Married. (Described in OWL, this subproperty  
> would have singleton classes as its domain and range.)
> 4. The RDF triple, considered as a platonic syntactic object, which  
> asserts (2). Again, there is no RDF equivalent, although some folk  
> use RDF reification for this (contrary to what the standard says;  
> but it does say it non-normatively)
> 5. A particular token or inscription of this triple in some  
> document: this is what an RDF reification is intended to denote,  
> according to the RDF semantics.

What we are after here is 2. or 3. I have to admit that I am clueless  
as to what the distinction between them is. The trouble may be that I  
don't see any difference between a fact of a marriage and the state  
of being married. I tried looking in Wikipedia, but, well, it didn't  
help. Any additional clues would be welcome.

> This would seem to depend on what 'reification' means in TM. Can  
> anyone tell me how to find this out? The description in http:// 
> www.isotopicmaps.org/sam/sam-model/#d0e991 is completely  
> incomprehensible.

It means either 2. or 3., but I don't yet know which.

> BTW, a singular lack in this ISO TM document is an explanation of  
> what is meant by "relationship", as in [...]

It's true that this is not defined beyond the use of a common English  
term. I understand that for the purposes of logic this is unlikely to  
be satisfactory.

> This could be understood as meaning a relation, as in sense (1)  
> above, or a fact (or proposition) as in sense (2), or possibly as  
> meaning a trope, as in sense (3), or possibly something else  
> altogether. It is impossible for me to determine what the document  
> actually means, and the term is not defined in it anywhere. Can  
> anyone point me at an explanation of what this terminology  
> ("relationship") is intended to mean in TM?

There is none.

> A related question: is there any kind of formal semantics for TM?  
> Without one, no suggested mapping between TM and RDF can be  
> authoritative.

There is no formal semantics for Topic Maps. I understand your  
concern that this means mapping from something that has no logical  
interpretation to something that does, but this happens to be the  
situation we are in. I think it's worth bearing in mind that this  
will be the case when mapping to RDF from pretty much any existing  
technology, so this is not a failing that's unique to Topic Maps.

Lars Marius Garshol, Ontopian               http://www.ontopia.net
+47 98 21 55 50                             http://www.garshol.priv.no
Received on Friday, 24 March 2006 09:27:37 UTC

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