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#95: Development of CF 1.5 Data Model
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  Reporter:  markh           |       Owner:  [email protected]
      Type:  task            |      Status:  new                          
  Priority:  medium          |   Milestone:                               
 Component:  cf-conventions  |     Version:                               
Resolution:                  |    Keywords:                               
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Comment (by taylor13):

 Hi all,

 Just to note one use case (CMIP5 specifications) where, perhaps
 mistakenly, it was assumed that attributes appearing both as global and
 (with different text) as variable would be concatenated to provide more
 complete information.  The assumption wasn't that if the variable
 attribute was present it would supersede/override the global one.  Note
 that the description below distinguishes between types of information that
 might appear in comment and history attributes which would be common among
 variables vs. different from one variable to the next.

 Here's the description of the relevant CMIP5 attributes taken from http
 ://cmip-pcmdi.llnl.gov/cmip5/docs/CMIP5_output_metadata_requirements.pdf :

 CMIP5 optional GLOBAL attributes:

 comment = A character string containing additional information about the
 data or methods used to produce it.  The user might, for example, want to
 provide a description of how the initial conditions for a simulation were
 specified and how the model was spun-up (including the length of the spin-
 up period).

 history = A character string containing an audit trail for modifications
 to the original data.  Each modification is typically preceded by a
 "timestamp".   The "history" attribute provided here will be a global one
 that should not depend on which variable is contained in the file.  A
 variable-specific "history" can also be included as an attribute attached
 to the output variable.

 CMIP5 optional VARIABLE attributes:

 comment = a character string providing further information concerning the
 variable (e.g., if the variable is mrso (soil_moisture_content), the
 comment might read "includes subsurface water, both frozen and liquid, but
 not surface water, snow or ice").

 history = a character string containing an audit trail for modifications
 to the original data (e.g., indicate what calculations were performed in
 post-processing, such as interpolating to standard pressure levels or
 changing the units).  Each modification is typically preceded by a
 "timestamp".  Note that this history attribute is variable-specific,
 whereas the global history attribute defined above (see "Optional
 attributes" under "Requirements for global attributes") provides
 information concerning the model simulation itself or refers to processing
 procedures common to all variables.

 Don't know if this is helpful, but thought I'd pass it along.

 Best regards,
 Karl

-- 
Ticket URL: <https://cf-pcmdi.llnl.gov/trac/ticket/95#comment:89>
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