[sc34wg3] Towards TMDM 3.0
rani.pinchuk at spaceapplications.com
Mon Feb 23 08:03:25 EST 2009
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
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
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.
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.
Space Applications Services
Tel.: + 32 2 721 54 84
Fax.: + 32 2 721 54 44
More information about the sc34wg3