[topicmapmail] XTM-RDF conversion

[Dichev, Christo]

Hi Lars Marius,

Thank you. We know that work. In fact our starting point was the "Living
with topic maps and RDF" along with the  "A Survey of RDF/Topic Maps
Interoperability Proposals" and the "Guidelines for RDF/Topic Maps
Interoperability" plus the existing approaches oh TM-to-RDF mapping.

However since different opinions were expressed by  Peter F.
Patel-Schneider, the ODM team, Leo Obrst, etc.  on Topic Maps-to-RDF
mapping we wanted to see if there is a somewhat a consensual view on
such arguable issues within the Topic Map community.

Christo 

-----Original Message-----
From: topicmapmail-bounces at infoloom.com
[mailto:topicmapmail-bounces at infoloom.com] On Behalf Of Lars Marius
Garshol
Sent: Monday, June 11, 2007 3:13 AM
To: topicmapmail at infoloom.com
Cc: Boriana Ditcheva
Subject: Re: [topicmapmail] XTM-RDF conversion

Hi Darina,

* Dicheva, Darina
>
> We are currently implementing an XTM-RDF conversion for TM4L. In this 
> relation, I would like to ask for an opinion on translating  TM 
> associations.

This problem is in my opinion already solved. An algorithm for such
conversion is given at

   http://www.ontopia.net/topicmaps/materials/tmrdf.html#N1024

and is implemented in the OKS Samplers, so you can try it out for
yourself. (Just use "Export" and select RDF/XML.)

A set of PSIs that can be used to guide the conversion are defined at
   http://psi.ontopia.net/tm2rdf/

> The problem is that RDF is built on directional binary relations:
> Subject-Property-Object, while in TM a binary association  authorship 
> has five elements:
>
> authorship(author: Shakespeare, work: Hamlet).

The natural translation of this in RDF is in my opinion:

   has-author(hamlet, shakespeare)

The roles are just an artifact of how the information is expressed in
Topic Maps, and are not needed in RDF.

> Currently we are thinking of translating such an association as
>
> 	Author -- wrote -- Work
>
> but are wondering whether to include also the reverse part of the 
> relationship in the translation:
>
> 	Work -- written-by -- Author
>
> How would including it, or not including it, affect RDF 
> completeness/readability/inference capability?

You don't need to include it, since the question of what the inverse is
is one that exists for every RDF statement. OWL lets you handle this (if
you want) by explicitly stating that one property is the inverse of
another, as in

   wrote owl:inverseOf written-by

> Clearly, if we want to represent both directions, we'd have to make 
> two statements per every association instance: [...]

Actually, if you use owl:inverseOf then software can infer the inverse
statements. Not all software does, but in theory it could, and in
practice it often does.

> Would that be undesirable?

I think so, yes. It's better to just state it once.

> There are, of course, other more thorny issues related to scope and 
> variants, but piece-by-piece.

Yes. Scope and variants is harder. :)

--Lars M.

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