[topicmapmail] Interpretive Difference between Occurrences and SI or SL

[Lars Marius Garshol]

* Tobias Redmann
>
> What is the interpretive difference between occurrences and subject
> indicators or locators. Both uses URIs to indicate relevant resources.
> You can use both to get the related topic.
>
> The subject indicator describes the subject, but there are a lot of
> cases where the indicator is the one and only occurrence of the topic.
> Every occurrence is in some way relevant to the subject. So adding a
> type "description" or "indicator" to an occurrence mean the same.

Not really. It goes like this:

  - subject locator: the resource *is* the subject of the topic
  - subject indicator: the resource describes the subject of the
                       topic *unambiguously*; most likely the
                       resource is not interesting to an end-user
  - occurrence: the resource has information about the subject of
                the topic in some way, and is suitable for an
                end-user

So in the first two cases the connection between the subject and the  
resource is very close, whereas in the third case it need not be.

A description is not the same as a subject indicator, although  
admittedly they share some features. A description would be very poor  
if it did not tell you what the subject was, but it doesn't  
necessarily do this unambiguously, and it's meant for an end-user  
more than for someone developing Topic Maps solutions.

In general, the whole situation is different, because when you use a  
subject indicator what you want is really an *identifier* for your  
subject, and that's generally more important than the content of the  
indicator. When you add a description you're only interested in the  
*content*.

> This also leads to the question: What to do with topics where the si
> equals the occurrence and how to model them? What means this?

If you find a case where this happens you have a dubious topic map.  
Why does the subject indicator contain information that's relevant to  
a different topic? It should just be a short and sweet unambiguous  
definition of the subject, not some long discursive piece that  
rambles over different subjects.

I hope that helped.

--Lars M.