[tdwg-guid] Globally unique vs. globally locatable

Ricardo Pereira ricardo at tdwg.org
Wed Jun 13 18:52:55 CEST 2007

    Hi folks,

    Here is another issue from that discussion thread that I'm 
splitting: (simply) globally unique vs. globally locatable. As Chuck said:

1. An identifier that is simply globally unique - that is, the id is never duplicated and always refers to the same thing.  So, you can use it as a unique reference in a paper, like an ISBN/ISSN number. But more importantly, it also can be used in data files/serialized XML to enable computers to quickly compare import/export records for merge/update, which is an important function to many, many biodiversity data projects.  But, this id does not itself tell you where it can be found.  Its location must come from another source.

2. An identifier that is globally locatable via the Internet - that is, the id is never duplicated and always locates the same thing (with a further definition needed of what the thing is).  The globally locatable identifier needs to be locatable by a web browser (HTTP) but more importantly also by web services which may want to use a different protocol.  

    I would argue that, without loss of generality, any identifying 
scheme considered by this group (LSID, DOI, Handles, ARK and any HTTP 
URL based scheme) fulfill both use cases. Since we are interested in 
sharing data, the 2nd use case is far more important for us than the 
first. For that reason, I would suggest that any other scheme that 
provide globally unique but non-locatable identifiers (i.e. that fulfill 
use case #1 but not #2) would be irrelevant to this group.

    Such a scheme would still be important for cases other than sharing 
data, but that discussion would be outside of the scope of this group.

    If you are interested in discussing the best way to make your local 
identifiers globally unique (which was the issue that started this 
discussion I suppose), that's the subject of another (very relevant) 
thread. For now the only thing I'll say about that is that there are 
guidelines for making local identifiers globally unique in each 
identifying scheme. In the particular case of LSIDs you may find 
information about that in the following documents:

* The LSID Specification - http://www.omg.org/cgi-bin/doc?dtc/04-05-01)
* LSID Best Practices (Naming conventions) - 
* LSID Namespaces discussion - 

    In any case, rest assured that we will sum up all those guidelines 
into a section of the Bratislava Declaration ;)



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