[Go-essp-tech] versions, checksums and the TDS

[Karl Taylor]

Dear all,

Concerning:

On 9/24/11 4:35 AM, Estanislao Gonzalez wrote:
> 2) checksums
> They are the only reference to the outside that a data node give of the
> changes a file suffered from one version to another, i.e. for
> replication we use that information to retrieve only files that change
> from one version to another. The same principle could be applied for
> tools designed for end users.

without disputing that checksums should be mandatory, I want to point 
out that a user who has lost the checksum associated with a file he has 
downloaded shouldn't have to recompute the checksum to determine whether 
his file is a copy of a file residing at the datanode.  Recall that 
recorded in each netCDF file is a unique tracking_id, which I'm almost 
positive is also in the thredds catalog.  It will certainly be quicker 
for the user to read the tracking_id and then check whether it matches 
the latest version.  I think we want to maintain tracking_id as an 
option for checking whether new files exist in a new version.

best regards,
Karl
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