Hi Nan:
I reviewed the findings of the 2015 NASA ESDSWG group on Virtual Collections
and they were a set of use cases (including similar to yours) with some
capabilities for solutions including THREDDS aggregations and event-based
search capability for datasets (and implicitly granules for those datasets). So
your proposal on virtual THREDDS aggregations seems a good path forward. But
it would likely need manual curation to maintain as new granules are created.
On 9/19/18, 2:09 PM, "Armstrong, Edward M (398G)"
<Edward.M.Armstrong@xxxxxxxxxxxx> wrote:
Hi Nan:
I didn't think about THREDDS virtual aggregation but that might be an
approach that works.....
A few years ago there was a NASA ESDSWG on this subject (virtual
collections). I'll look back and see if there are any recommendations that
could help. I believe this type of THREDDS aggregation was one of them.
On 9/19/18, 12:47 PM, "Esip-documentation on behalf of Nan Galbraith via
Esip-documentation" <esip-documentation-bounces@xxxxxxxxxxxxxxxxx on behalf of
esip-documentation@xxxxxxxxxxxxxxxxx> wrote:
Thanks Ed, Dave, and Aleksandar.
These are all possibilities, although I was hoping there would be an
attribute
in some convention, somewhere, that was more specific. Both
'references',
and 'metadata_link' seem to be intended to provide information about
the
NetCDF
file in which they're found, and 'external_variables' is meant to list
'variables which
are named by attributes in the file'.
What we were hoping to do was point to external data that was collected
at the same
place and time as the data in the file, but which is not IN the file
for
various reasons.
This might be because it's not time series data, or because it's from
another domain
where NetCDF is unknown.
Making this information machine-readable would require it to be pretty
specific, and
might even require more than one attribute - one giving the location,
one describing
the remote content, and maybe one describing how the data sets are
related.
Maybe the terminology that THREDDS uses would be a good place to start.
I think
I've got some THREDDS documentation ... somewhere around here. Also,
NcML has the
concept of Aggregation (to create "virtual" NetCDF datasets, according
to the NcML page
at unidata), but I'm not sure how far that's gone since I last looked
at it.
Thanks again -
Nan
On 9/19/18 11:48 AM, Aleksandar Jelenak via Esip-documentation wrote:
> Hello!
>
> There's also this:
>
http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#external-variables
>
> Apparently this approach is chosen for the CMIP6 data and is lax on
> the specifics by design. The context where to find files with those
> referenced external netCDF variables is to be provided in some
> unspecified manner.
>
> It is possible to include links to related files on THREDDS dataset
> pages but this is outside of file. The metadata_link keeps the
> connection in the file but requires that the application code handle
> ISO XML.
>
> -Aleksandar
>
>> On Sep 19, 2018, at 11:32 AM, Armstrong, Edward M (398G) via
>> Esip-documentation <esip-documentation@xxxxxxxxxxxxxxxxx
>> <mailto:esip-documentation@xxxxxxxxxxxxxxxxx>> wrote:
>>
>> Hi:
>> I would recommend the ACDD attribute “references”:
>> references
>>
>> Published or web-based references that describe the data or methods
>> used to produce it. Recommend URIs (such as a URL or DOI) for papers
>> or other references. This attribute is defined in the CF conventions.
>>
>> In CF global attributes there is also a “comment” attribute where
>> such info could be placed in a generic sense.
>> I have often thought of this use case too and its an area where ACDD
>> or CF could be improved.
>> The metadata_link could point to an ISO 19115 record where multiple
>> citations could point to other datasets cleanly.
>> *From:*Esip-documentation on behalf of David Neufeld
>> *Reply-To:*David Neufeld <david.neufeld@xxxxxxxx
>> <mailto:david.neufeld@xxxxxxxx>>
>> *Date:*Wednesday, September 19, 2018 at 8:18 AM
>> *To:*Nan Galbraith <ngalbraith@xxxxxxxx <mailto:ngalbraith@xxxxxxxx>>
>> *Subject:*Re: [Esip-documentation] [thredds] information on related
files
>> Hi Nan,
>> I'd recommend using a 'metadata_link' attribute.
>>
http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_1-3#Additional_Metadata:_metadata_link_attribute
>> -Dave
>> On Wed, Sep 19, 2018 at 8:56 AM, Nan Galbraith <ngalbraith@xxxxxxxx
>> <mailto:ngalbraith@xxxxxxxx>> wrote:
>>> Hi ESIP, NetCDF, and THREDDS folks -
>>>
>>> First, I'm sorry for the cross posting. I have a hard time figuring
>>> out which NetCDF list does what; there are 'best practices' threads
>>> on several lists, interspersed with install and development threads.
>>>
>>> The OceanSITES project would like to find the most useful way to
>>> provide a link within a NetCDF file to an external dataset.
>>>
>>> > Another piece I am missing ... is an optional field, that link to
a
>>> > data DOI. Why? Here's an example: We operate an OceanSITES site
off
>>> > the Cape Verdes and the sediment trap data is ... not included in
an
>>> > netcdf file but processed and stored elsewhere
>>> >https://doi.pangaea.de/10.1594/PANGAEA.863969
>>>
>>> Does THREDDS have a standard way to provide links to related or
>>> co-located data? Is this something we discussed as part of ESIP's
>>> ACDD recommendations? I've been searching through my store
>>> of old messages, and haven't come up with anything.
>>>
>>> Thanks very much for any advice on this!
>>>
>>> - Nan Galbraith
>>>
>>>
>>>
--
*******************************************************
* Nan Galbraith Information Systems Specialist *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 (508) 289-2444 *
*******************************************************
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