I like Bryan's recommendation for a UUID or similar.
Now I'm going to be annoying and suggest the UUID *could* be a URI, or
these days, an IRI (International ..).
And I think the way of 'locating' the file should be neither in
packaging nor in local resolution; it should be in global namespace
resolution. This is the way of the future, and is already more
'permanent' than either packaging or local resolution, IMHO.
There is one form of URI in particular that is already resolvable: a
URL. OK, that's an old song, but I'm gonna stick to it for a while
longer. That form meets all the other requirements: it can be
registered in a resolver, it can be guaranteed unique (to the same
authority level as a UUID, anyway), and it is a unique string that can
be used to validate the link). And it has the obvious benefit of
being resolvable right now, for as long as the domain is held and
properly maintained (Good URLs don't die).
Since the last paragraph risks starting another unique identifier war,
I promise not to re-engage unless someone asks me to. Meanwhile, I like
John
On Nov 19, 2009, at 22:23, Bryan Lawrence wrote:
> On Thursday 19 November 2009 19:40:08 Jonathan Gregory wrote:
>>> ... In some cases, referencing attributes such as
>>> "coordinates" and "ancillary_variables" would, ideally, point
>>> to a
>>> variable in a different dataset.
>>
>> This is a general problem to which CF doesn't have a solution
>> because it was
>> conceived as a convention for single netCDF files. However we need
>> a solution
>> as often several files should be treated as a single dataset.
>>
>> If the files don't overlap i.e. their contents are complementary, I
>> think it
>> should be satisfactory to allow variables in one file to be pointed
>> to by name
>> from another file, with no other mechanism being required within
>> the file. I
>> don't like the idea of naming one file within another file, as that
>> would be
>> very fragile. Instead, I think the file aggregation should be
>> implied by
>> simply defining the group of files which are to be treated as one
>> file e.g.
>> by putting them in one directory.
>
> It's the old ones that are the best ones :-) :-) this issue keeps
> on coming back ... :-) :-) and we keep trying to ignore it ...
>
> I think we agree that an actual physical filename including path is
> useless. We need both a relative link which relies on the
> preservation of a group of files in a particular arrangement ...
> AND an internal identifier so more robust linking mechanisms can be
> used when (if) the data ends up in a managed environment.
>
> I think it's crucial in this situation to ensure that each file has
> a unique identifier within it (created, for example, with uuid),
> because all solutions which rely on packaging are fragile (SAFE is
> probably better than most), but the bottom line is that users move
> files around ... and we need some way of ensuring that we/they can
> validate the links that are in place are the ones that were
> originally intended.
>
> So relative links would also include the identifier of the intended
> target as well as the relative path in operating system agnostic
> terms.
>
> That identifier can be used in two ways: to validate the link (my
> software can always check that the variable that I just opened
> following a link from another one is the one that was expected by
> checking the container identifier), and b) to produce an identifier
> resolver service for the situation where the packaging has had to be
> broken (which might occur for performance reasons or ...)
>
> CF could recommend something like this ...
>
> Bryan
>
> --
> Bryan Lawrence
> Director of Environmental Archival and Associated Research
> (NCAS/British Atmospheric Data Centre and NCEO/NERC NEODC)
> STFC, Rutherford Appleton Laboratory
> Phone +44 1235 445012; Fax ... 5848;
> Web: home.badc.rl.ac.uk/lawrence
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
--------------
I have my new work email address: jgraybeal at ucsd.edu
--------------
John Graybeal <mailto:jgraybeal at ucsd.edu>
phone: 858-534-2162
Development Manager
Ocean Observatories Initiative Cyberinfrastructure Project:
http://ci.oceanobservatories.org
Marine Metadata Interoperability Project:
http://marinemetadata.org
Received on Fri Nov 20 2009 - 00:53:42 GMT
