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Re: RDFTM: RDF reification

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 24 Mar 2006 01:07:14 -0800
Message-Id: <p0623090fc0489d6a42cb@[192.168.1.219]>
To: "Steve Pepper" <pepper@ontopia.net>
Cc: "Lars Marius Garshol" <larsga@ontopia.net>, "RDFTM editors" <rdftm@ontopia.net>, "SWBPD list" <public-swbp-wg@w3.org>

>[Regarding the issue of whether reification has the same
>semantics in Topic Maps and RDF]

Sorry, I have only just seen this thread.

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.

>  Basically, the use case is to be able to state marriages as a
>  single triple (for convenience, say), while still retaining
>  the ability to talk about the marriage, and retaining the
>  connection between the triple and the marriage node.

Trying to understand this, it seems that there 
are several notions involved. Let me try to 
disentangle them, to help me understand what you 
want and how best to deliver it.

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 remains is to figure out how to express TM reification if we 
>| can't just use normal RDF reification.

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.

BTW, a singular lack in this ISO TM document is 
an explanation of what is meant by 
"relationship", as in
-----
3.1
association

representation of a relationship between one or more subjects
-----
(from http://www.isotopicmaps.org/sam/sam-model/#terms-and-definitions)

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?

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

Pat Hayes


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Received on Friday, 24 March 2006 09:07:24 GMT

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