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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 jonathan): Dear all Replying to [comment:98 bnl]: > I think the global/variable attribute as currently formulated does not allow an unambiguous resolution, and so the data model cannot either. The data model is about data variables (fields), not about files. A field has only one property of a given name (source, etc.). So if it were decided that the current convention is ambiguous about how global and variable attributes in a netCDF file are to be treated, the data model could not say how the contents of the relevant property should be derived from the netCDF attributes. Is that right? That seems rather unsatisfactory to me. Karl proposes we ''change'' the convention so it doesn't mention "precedence". I agree, that would be a change. I think the current convention is actually clear. If there is a variable attribute, the global attribute should be ignored. That's what "precedence" means. However, Karl and Nan have given examples where the information in the global and variable attributes need to be combined, so clearly this situation has to be taken seriously. I would say these datasets were not written correctly according to any existing version of the convention, so we don't have to allow for it in the present data model. There are two things we can do, however. * Acknowledge that this situation exists, and recommend that software should have options to combine the attributes upon reading them in. This behaviour should be optional, because there may also exist datasets written on the assumption that variable attributes override global attributes, as was intended (I believe). The user of the data will have to decide which treatment is appropriate. * Clarify the convention in the next version to avoid this problem for future data. That should be the subject of a different ticket, because this ticket is about the data model for CF 1.5. Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:99> 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.
