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Clarification of rules for positioning comment and interval in cell methods strings #274
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I agree with @martinjuckes that the conformance document has the intended interpretation. If that it is so, the text of the convention could be clarified as a defect issue. |
I think I prefer having the optional (and sometimes non-standard) parenthetical information coming at the "end of the phrase identifying the method"; breaking up the main elements of the method seems unnecessary. I would prefer, for example "mean where sea_ice (and in the immediate vicinity of polar bears)" to "mean (in the immediate vicinity of polar bears) where sea_ice". |
@taylor13 : apologies for the long silence on this issue. With the approach your approach, would you permit multiple comments, e.g. I can see the attraction of making a mis-placed comment a warning rather than an error, but we need to be sure that it does not introduce more complexity for software parsing the strings. |
I hadn't thought of that being necessary. On reflection, I don't really see a need to allow the parenthetical information to appear anywhere except at the end of any phrase specifying a method (but of course each method phrase could have parenthetical information, so multiple parenthetical statements could occur in cell_methods). Thus, in your example above you might have: I agree we should worry about difficulty parsing, but don't think anything discussed above would be too difficult. |
The discussion of this issue indicates that it should be addressed as a defect in the conformance document, so I am changing the label accordingly. |
Dear @martinjuckes Thanks for raising this issue in 2021. No objections were raised, and enough support was expressed to approve this proposal. It requires a PR to change the first sentence in Sect 7.3.2, for which you've already suggested wording. Are you able to prepare a PR? Best wishes and thanks Jonathan |
One of the contributors to the CMIP6 archive has contributed data with a
cell_methods
string of the form:area: time: mean (interval: 1 month) where sea_ice
. CF Checker 4.0.0 reports this as an errorERROR: (7.3): Invalid syntax for cell_methods attribute
.The relevant paragraph of the convention, the first in sub-section 7.3.2, states that "To indicate more precisely how the cell method was applied, extra information may be included in parentheses () after the identification of the method." The author of the data file is interpreting the reference to "after the identification of the method" as meaning directly after
mean
in thecell_methods
string. This is consistent with the usage of the word "method" throughout section 7.3.The conformance document, on the other hand, specifies that the the parentheses should come at the end of the phrase specifying the method, i.e.
area: time: mean where sea_ice (interval: 1 month)
, and the CF Checker, as we expect, follows the conformance document.My personal preference would be to follow the interpretation of the conformance document, provided this is consistent with the original intention of the sub-section in 7.3, but this would, I believe, require some clarification of the text, e.g. "To indicate more precisely how the cell method was applied, extra information may be included in parentheses () at the end of the phrase identifying the method."
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