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#95: Development of CF 1.5 Data Model -----------------------------+---------------------------------------------- Reporter: markh | Owner: [email protected] Type: task | Status: new Priority: medium | Milestone: Component: cf-conventions | Version: Resolution: | Keywords: -----------------------------+---------------------------------------------- Comment (by davidhassell): Hello, > > I interpreted 'takes precedence' to mean that the data variable attribute was to be treated as > having primacy, having more import than the global variable attribute. This is different from > saying that the global attribute in this case: has no meaning / is overridden / is ignored, if > a data variable has an variable attribute with the same name. > However, how can we discern the case where the data variable's attribute really is meant to entirely replace the global value? An example might be a global `source` attribute having the value `'Unified model'` and the file contains a data variable (containing data from another model) which has a `source` attribute of `'ARPEGE'`. This example suggests to me that the "precedence" we are talking should mean "overrides". If I understand it correctly, the very useful (thanks, Karl) CMIP5 strategy neatly sidesteps this issue by i) insisting that common global and data variable attributes should contain information of pre-defined types and are mutually exclusive and ii) disallowing certain global attributes as data variable attributes (such as source). But I don't think that this is an option available to us at the moment for CF-netCDF in general. It'd be nice to somehow support both views, I'm not sure how we could do that. I don't think that this issue has any bearing on the question of whether or not global attributes should be stored separately to data variable attributes in the data model. Whether you "combine" or "override" in the conventions - the end result is still just some metadata on the field. The data model is solely about describing the logical information content of a field, but that doesn't, and shouldn't, stop a software library from storing extra information for, for example, writing out fields to CF- netCDF in a particular, arbitrary way. All the best, David -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:92> CF Metadata <http://cf-pcmdi.llnl.gov/> CF Metadata This message came from the CF Trac system. To unsubscribe, without unsubscribing to the regular cf-metadata list, send a message to "[email protected]" with "unsubscribe cf-metadata" in the body of your message.
