[sc34wg3] Towards TMDM 3.0

Rani Pinchuk rani.pinchuk at spaceapplications.com
Mon Feb 23 08:03:25 EST 2009

Dear Lars,

I am not sure that I understand this.

You say that an item identifiers can be used to refer to topics, but 
actually, if I understood correctly, according to you, item identifier 
can be used to refer indirectly to a subject. So, all topics having the 
same item identifier must be a proxy to the same subject (so they should 
be merged).

That is, all topics in different topic maps, having the same item 
identifier must be a proxy to the same subject.

Why do we need this? What this kind of identifiers give us, that PSIs do 
not give?

I thought that an item identifier allows us to refer to a specific topic 
  and not to a group of topics. After all, it might be useful to be able 
to refer somehow to one of the topics that are about to be merged.

Kind regards,


Lars Marius Garshol wrote:
> * Rani Pinchuk
>> Why do we do that? What is the use of collecting item identifiers from
>> different topics (in possibly different topic maps) to the current one
>> if they have no uniqueness outside of the topic map? How can we use
>> those item identifiers?
> Item identifiers can be used to refer to topics, just like subject  
> identifiers. And, just like subject identifiers, they are not unique  
> across topic maps.
> We try to avoid having two topics for the same subject in different  
> topic maps, because that's just bad data. However, if we want to  
> represent a subject in two different topic maps we have no choice: we  
> *must* have two different topics. There's just no other way to do it.
> Now, let's say that A is a URI, and it's the PSI for the "person"  
> topic type. If I've created the "person" topic type in two different  
> topic maps, of course I want both topics to have this PSI attached to  
> them, to connect both topics to this shared topic type.
> The same argument applies for item identifiers. If I know that B is  
> the item identifier for some topic T, then I want all topics in the  
> universe which represent the same subject as topic T to have B  
> attached as an item identifier, because this facilitates merging,  
> lookup, and so on.
> There's nothing special about what happens with item identifiers in  
> clause 6.2 (after all, the same thing happens with subject identifiers  
> and subject locators), and there's nothing special about clause 6.2,  
> either. Item identifiers (and other identifiers) are not unique across  
> topic maps because *topics* are not unique.

Rani Pinchuk
Project Manager
Space Applications Services
Leuvensesteenweg, 325
B-1932 Zaventem

Tel.: + 32 2 721 54 84
Fax.: + 32 2 721 54 44


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