philosophical question about occurrences

Hi everyone,

I'm in the process of writing my MA-thesis, which has a good deal to do  
with topic maps. In one chapter I present the paradigm's major  
concepts. While writing about occurrences, something struck me: the  
literature usually says that occurrences ARE the resources that topics  
refer to. So, I thought, resources are called (or turned into)  
occurrences once they are referenced by a topic. Steve Pepper indicates  
this in his TAO-Article: "A topic may be linked to one or more  
information resources that are deemed to be relevant to the topic  
insome way. Such resources are called occurrences of the topic.". The  
same is indicated by the XTM-specification: "An occurrence is any  
information that is specified as being relevant to a given subject."

However, occurrences can be scoped. The same resource  - let's say a  
fictional piece of text - could be occurrence for two or more topics -  
let's say two characters appearing in it. Character Paul is the main  
character in the story, while Peter is a side character. I could scope  
the occurrence with "main character" for topic 'Paul' and with "side  
character" for topic 'Peter' (The example might not be a good one, but  
technically this is possible). But, what I have actually done, is  
scoping the _reference_ to the resource, not the resource itself. Which  
scope I choose is dependent on the topic the resource is referred from.  
So, if we say we can scope occurrences, are occurrences really the  
resources themselves, or are they references to the resources? The same  
problem appears in connection with occurrence types: If I type an  
occurrence as 'mention', I really type its reference. Holger Rath  
indicates this in an article(1) from 2001: "An occurrence is the link  
to an information [...] - it connects the topic domain with the  
resource domain."

I hope this wasn't all to confusing and meaningless. Maybe the question  
is totally irrelevant (and hopefully it hasn't been answered a thousand  
times before...), but I would be interested in what other people think  
about it.

Thanks for reading this! Cheers,

Knud

1: Semantic Resource Exploitiation with Topic Maps
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Knud Möller -  Institut für Sprachliche Informationsverarbeitung,
Universität zu Köln
(Department of Linguistic Data Processing,
University of Cologne, Germany)