[sc34wg3] Towards TMDM 3.0

[Rani Pinchuk]

Dear Lars,

Throwing the item identifiers after a merge is exactly what I suggest: I 
suggest to simplify things by having a mandatory one item identifier per 
item. The item identifiers are not used for merging, only for 
identifying items. And no collection of item identifiers is done after 
merging.

This is why I would like to ask you to explain in more details your 
three reasons.

For (1) - with your suggestion, indeed all topics have a "kind of 
identifier" but it is actually a subject identifier, as it is not item 
identifier (although it is called that way). The reason it is not item 
identifier, is that it does not help you to identify one item but a 
group of items (because we collect the item identifiers, we do not have 
any more one item identifier - one topic relationship).

For (2) - Let's examine a concrete example:
Suppose we have a topic map with a topic with id "person" and item 
identifier http://one/person.
We have a query to show all persons (pseudo code of course):
    show all topics of type "person".

I assume here that we do not use the full item identifier in the queries 
we write.

Now we merge with another topic map, that has other persons, and are 
typed with a topic with item identifier http://two/human

If we still use topic map http://one we still can use our query. If we 
now use topic map http://two, we cannot, because we use an ID in our 
query that does not match to "human" and cannot be extracted from the 
other item identifier.

So I cannot see any gain here.

A much simpler way to achieve the same is to simply keep the local item 
identifiers when merging with external topic maps. The collection of 
item identifiers does not help.

For (3) - This is indeed a rare situation. If A and C are merged, it 
means that we had a reason to merge them. The same with B and C. Only if 
those merges were done without PSIs, merging A and B using item 
identifiers will actually make any sense. Merging without PSIs seems to 
me at least as difficult as assigning PSIs to the topics that should be 
merged.

Thanks again,

Rani

Lars Marius Garshol wrote:
> We could of course throw away item identifiers after the import, but  
> have decided not to, for a number of reasons.
> 
>   (1) It means all topics can have some kind of identifier, without
>       this having to be a subject identifier, which is useful in a  
> number
>       of situations, from CXTM testing to web service protocols.
> 
>   (2) It means you can refer to topics that don't have a PSI or subject
>       locator. When people write queries that use IDs to refer to
>       topics that's because preserving item identifiers means you still
>       have the IDs available.
> 
>   (3) It helps with merging, in a few, very limited cases, like when
>       you're merging a.xtm with b.xtm and both of those include a
>       common c.xtm.
> 
> --Lars M.
> http://www.garshol.priv.no/blog/
> http://www.garshol.priv.no/tmphoto/
> 
> 
> 
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> sc34wg3 mailing list
> sc34wg3 at isotopicmaps.org
> http://www.isotopicmaps.org/mailman/listinfo/sc34wg3

-- 
Rani Pinchuk
Project Manager
Space Applications Services
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