[sc34wg3] Towards TMDM 3.0
rani.pinchuk at spaceapplications.com
Tue Feb 24 05:49:30 EST 2009
I am sorry to persist, this is still not clear to me.
Lars Marius Garshol wrote:
>> Why do we need this? What this kind of identifiers give us, that
>> PSIs do
>> not give?
> The reason these identifiers exist at all is in order to handle topic
> IDs and topicRefs in XTM. Firstly, the specs need to be able to
> resolve topicRefs and make sure they match up. Secondly, in most cases
> this is the only form of identity a topic has, and so in order to
> ensure that merging works these identifiers have to be preserved.
> The [item identifiers] property is separate from the [subject
> identifiers] property simply because item identifiers are lower-grade
> identifiers than subject identifiers, and we do not want to mix the
> two types of identifiers up.
If I understand correctly, you say that usually item identifiers are not
used as subject identifiers, but when there are no subject identifiers
we have to have something in order to merge, so we use item identifiers.
I find this dangerous. Many topics might be merged by mistake (some IDs
might be popular defaults given by the Topic Maps engine. "1" for
example. Other might be simply confusing choices. "bank" for example).
I would actually prefer to merge by names which seems to me much more
safe. Or, to use more sophisticated algorithms for merging (e.g. using
>> I thought that an item identifier allows us to refer to a specific
>> 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.
> Defining an identifier that is guaranteed to be unique across all
> topic maps is not going to be easy, and in any case it's hard to see
> any clear benefit in it. After all, identifying the topic map + giving
> a topic identifier will do the same thing today.
I understand from what you write that ID in XTM is an item identifier
without the topic map IRI. Is this correct?
At first, I thought that the item identifier includes the topic map IRI,
and therefore you could claim that the item identifiers are unique.
All in all, I find that the model you describe above is very confusing:
item identifier actually identifies subject, but on a lower grade then
subject locators and identifiers.
Now, after understanding why we collect item identifiers when merging, I
would like to suggest to stop collecting those, and simply have one item
identifier per item, which identifies the item, not the subject. This
will be mapped to the ID of the XTM, and that's it.
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