[Esip-documentation] ACDD 2-3 question (geospatiotemporal extent)

[John Graybeal via Esip-documentation]

Steve,

Thanks for this.  Did you see my attempt to address the same point, in the added section called "Maintenance of Metadata in Derived Products"?  I am not arguing against your text, which is also good, but asking that you first consider my previously offered text, over which is based on words you and others had provided. I would appreciate your suggestion of an optimal set of changes (sorry for asking for extra work).

> ACDD attributes describe the granules that they are contained in. As data are processed (e.g., through subsetting or other processes), these characteristics can change. It is the responsibility of the processor to update these attributes as part of the processing. That said, some software processes and user practices modify the data without appropriately updating the metadata attributes. Given this reality, users are encouraged to verify critical attribute values, and understand how the data were processed, to be confident you are not using 'stale' metadata.

I think the recommendation for the 'Please see' note could be applied to a large number of attributes, which is why I didn't add it to any. Any particular reason you chose those?

And for everyone to note, as a reminder: As a working tool, the page NetCDF Utilities Metadata Handling has been created to identify the state of play for how tools handle metadata attributes when processing files.

John

On May 21, 2014, at 16:18, Steve Hankin <steven.c.hankin at noaa.gov> wrote:

> 
> On 5/21/2014 12:20 PM, John Graybeal via Esip-documentation wrote:
>> Hi Anna,
>> 
>> As a significant driver I'll offer one opinion. Caveat emptor.
>>> 1. Is this the best version to be using? (They will NOT be using groups)
>> Arguably, yes it is the best version to be using, but it is not approved at this point. I would say the status is 'stalled in a mostly happy place' -- with one exception, I haven't heard any complaints about this current 'Working' draft, which has been around for many months now and has been carefully reviewed by at least one person.  I *think* that all that is required for approval is for Derrick Snowden (or someone he designates, ideally not the principle updater, hint hint) to call a discussion/next steps meeting, at which any remaining issues can be raised and resolved.
>> 
>> There is only one open issue under discussion, namely whether the adoption of summary metadata for geospatiotemporal ranges is good, tolerable, or bad. It is hard to know for sure whether that will be changed (I suspect it will not, just from comments so far). It is my hope that the fact all these attributes are *recommended*, not *required*, means that it will be acceptable to leave this material in, perhaps with precautionary language (a proposal for which has already been added).  We haven't had a discussion in the group yet about this topic.
>> 
> 
> Hi John,
> 
> The draft at http://wiki.esipfed.org/index.php/Attribute_Convention_for_Data_Discovery_%28ACDD%29_Working needs only minor editorial additions to address the open issue discussed above.  In the ACDD document the word "Recommended" alone does not make users aware of the conditions under which the geospatiotemporal  extent attributes may lead to internally contradictory file content.   Here is a suggested addition:
>  under "Alignment with NetCDF and CF Conventions" add ...
> Note that the geospatial and temporal extent of a CF dataset is self-documenting through its CF coordinate variables.  The intent of the ACDD geospatiotemporal extent attributes is to make it easier to infer this information from a file.  Since these attributes provide redundant information, they may create a risk of corrupted content.  The risk is highest for the time extents of files that are likely to be aggregated into longer time series, such as files output by numerical forecast models and in gridded satellite data products. 
> 
> under Recommended Global Attributes: time_coverage_start, time_coverage_end, and time_coverage_duration add ...
> please see note in the "Alignment with NetCDF and CF Conventions" section of this users guide
> This does not change the content or spirit of the ACDD document.  It merely informs users of trade-offs that they should be aware of.
> 
>     - Steve
> 

John Graybeal
jbgraybeal at mindspring.com



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