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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 Jim I am not quite sure what you mean by "container". Do you mean a file, perhaps, which contains fields? I believe that we have so far agreed in this ticket that the CF data model is concerned with fields. That's indicated by this text, which I think we have all been happy with e.g. in [https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:27 comment 27]: "The central concept of the data model is a field construct. A field construct corresponds to exactly one data array together with associated information about the domain in which the data resides (defined by spatio-temporal and other coordinates) and other metadata. This data model makes a central assumption that each field construct is independent." The reason for taking this approach is that we want the CF data model to apply to data which isn't stored in physical netCDF files. It might be served from some other kind of database or file format, even if presented as though it were netCDF to the application. Because the fields are independent, David and I think that each field has only one `comment` property, for instance. The CF standard says that variable attributes have precedence over global attributes, which I think means that the value of the field's `comment` property should come from the data variable's `comment` attribute, if it has one, disregarding the global `comment` attribute. If the data variable has no `comment` attribute, the property comes from the global `comment` attribute, if there is one. However, it's been pointed out by Karl and others that some files have been written on the assumption that both global and variable attributes simultaneously apply to the data variable. That is, in my view, an erroneous interpretation of the CF-netCDF standard, but it doesn't cause a problem for the data model, if we allow software implementations to combine the global and variable `comment` attributes in some way, if both exist, to obtain the `comment` attribute for the field. Thus, I think we can just have a single `comment` property for the field in the data model, and we can regard it as an issue for implementation how the value of that property is got from the netCDF file. Is your suggestion something like Mark's in [https://cf- pcmdi.llnl.gov/trac/ticket/95#comment:103 comment 103], which distinguishes information from global and variable attributes? Although that would be possible, it's not consistent with CF version 1.5. Mark's example mentions an attribute `responsible_authority`. This is not a CF attribute anyway, so the CF data model doesn't need to say anything about how it should be handled, except that it is legal to have such attributes, as David said in [https://cf- pcmdi.llnl.gov/trac/ticket/95#comment:102 comment 102]. Best wishes Jonathan -- Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:106> 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.
