[sc34wg3] Towards TMDM 3.0

Lars Marius Garshol larsga at bouvet.no
Mon Feb 23 06:09:29 EST 2009

* 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.

Lars Marius Garshol  |  Consultant
Bouvet ASA Sandakerveien 24C D11 Postboks 4430 Nydalen NO-0403 Oslo
Phone: +47 23 40 60 00 | Fax: +47 23 40 60 01 | Mobile: +47 98 21 55 50

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