[topicmapmail] relationships: one-way and two-way

[Kal Ahmed]

Hi Simon,

I think that the other major difference between RDF properties and TM
associations is that TM associations allow > 2 roles. This can often be used
to great effect when representing complex relationships. There are those who
argue that any n-ary relationship can be replaced by n binary associations,
but I think that this can loose important detail about the grouping of those
associations.

With regards to occurrences, we hit the problem of distributed authorship.
One of the key points about an occurrence is that you can use a resource
over which you have no control as an occurrence resource for a topic.
However, if you really do have full control over the resource and you want
the sort of architecture you describe in which the resource "has knowledge"
of the topics it is an occurrence of, I suggest that you instead reify the
resource (i.e. create a topic that represents the resource) and then use
associations rather than occurrences to connect the resource-topic to the
other topics in your topic map. This is a pattern that I have seen applied
quite widely and almost always it is applied only to resources that are
under the control of the same user (or group of users) as the topic map and
works best when the control of the resources and the topic map are
integrated into a single application. Usually a resource identifier is used
as the URI. This can be as simple as the URL used to get to the resource (in
XTM use the resourceRef element child of subjectIdentity for this - this
says that "This topic represents the resource at the URL in the XLink HREF
attribute"), or it can be an identifier from your CMS mapped into a URI (I
often use a private URN scheme for this).

Hope this helps!


Best regards

Kal
----------------------------------------------
Kal Ahmed, Founder, Networked Planet Limited
http://www.networkedplanet.com/

> -----Original Message-----
> From: topicmapmail-admin@infoloom.com [mailto:topicmapmail-
> admin@infoloom.com] On Behalf Of Simon Grant
> Sent: 12 March 2006 08:35
> To: topicmapmail@infoloom.com
> Subject: [topicmapmail] relationships: one-way and two-way
> 
> Hello from someone relatively new to Topic Maps.
> 
> I wanted to test out an insight.
> 
> I have read that one of the issues between RDF and TM is the way that
> relationships/associations are handled.
> RDF being based around one-way relationships does seem problematic,
> though it looks like OWL covers that.
> 
> I just realised that this could be seen as a great value in the topic
> - occurrence distinction.
> Within topics, associations are naturally defined so that the
> association has an independent existence, relieving individual topics
> of the burden of containing representations of what they are
> associated with and how.
> 
> But when it comes to occurrences, out there in the world, one can
> only claim, from one direction, that a particular resource is an
> occurrence of a topic. That resource itself is not part of the TM,
> and within the resource, one cannot expect to find any representation
> of the fact that it is an occurrence of a particular topic, according
> to a particular topic map.
> 
> Does that make sense? Apologies for any naivety or ignorance.
> 
> Simon
> 
> --
> Simon Grant  http://www.simongrant.org/home.html
> Information Strategies for Development http://www.inst.co.uk/
> Please continue to use my established e-mail address
> a (just by itself) (at) simongrant.org
> 
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