[topicmapmail] philosophical question about occurrences

[Michel Biezunski]

Dunker:

> 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.


The occurrence expresses how a piece of information is relevant
to a given subject. The same piece of information can be an
occurrence of different topics and each of them can be of a different
kind (occurrence type). The occurrence can be best described as a 
relation between a subject and a piece of information and expresses 
why the piece of information is relevant to the subject. The why 
can be further subdivided between the kind of relevance (occurrence 
type) and the domain for which it is relevant (occurrence scope). 
The distinction between what goes to occurrence type and what goes to 
occurrence scope is a matter of perspective. It is part of the work 
of the topic map designer to decide what values should be given 
to each of them.

To summarize, I agree with you that an occurrence is not a resource,
but describes how a given resource is relevant to a given subject.

Michel
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Michel Biezunski
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