[Go-essp-tech] Are atomic datasets mutable?

[Karl Taylor]

Hi all,

Another common case that we'll have to deal with in CMIP5 and which 
should be considered in defining what a "version" is:  For the future 
(so-called RCP) runs, CMIP5 calls for runs initiated from the end of the 
historical run and as part of the core set of expts., running to the end 
of the 21st century.  At a lower priority some of these runs will be 
extended to the end of the 23rd century.  Groups will likely carry out 
these simulations in stages, sending us the 21st century output long 
before the 22nd and 23rd century output becomes available.   The 
component time-periods are part of the same experiment and CMOR2 will 
write output into the same directory. 

I think the users will be confused if a new "version" of model output 
(that has been modified in some way) is indistinguishable from model 
output that has been simply extended.  Both of the following options 
will be confusing:

Option 1) 21st century data for the RCP4.5 future run is received and 
identified as version 1.  Then the continuation of that run to the end 
of the 23rd century is received and stored as version 2.  New users will 
have to download both version 1 and version 2 to get the complete run.

Option 2) 21st century data for the RCP4.5 future run is received and 
identified as version 1.   Then the continuation of that run to the end 
of the 23rd century is received and stored as version 2 along with a 
copy of the data already stored as version 1.  In this case a new user 
will get all the data by downloading version 2, but an old user who 
already downloaded version 1, won't know if what's in version 2 is a 
duplicate of the data he already has, or is replacement data which has 
corrected some problems in the earlier version.

I would suggest therefore that for a single experiment, it would be best 
from a user's perspective to not assign a new version to model output 
that simply extends a previous run.  We will have to find a method by 
which to advise old users who already downloaded data that the runs have 
now been extended.

Best regards,
Karl


stephen.pascoe at stfc.ac.uk wrote:
> Hi all,
>  
> The UKMO has flagged up a use case where an atomic dataset might 
> change over time without being a new version.  The example is the 1000 
> year piControl run where UKMO is likely to deliver it in several time 
> chunks and would want it to be published before the full run is 
> complete.  Since atomic datasets represent the whole time period these 
> datasets will grow over time.
>  
> I am tempted to say each addition to the dataset triggers a new 
> version that deprecates the previous one but UKMO wasn't too keen on 
> that.  Any ideas?
>  
> S.
>  
> ---
> Stephen Pascoe  +44 (0)1235 445980
> British Atmospheric Data Centre
> Rutherford Appleton Laboratory
>  
>
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