Question about Coordinate System

Hi, Listers.
 
I have a question of coordinate system after going through available documents. 
Correct me if I am wrong.  
 
Accodring to the CF-Convnetions, parameters such as projection approaches (eg. 
Lambert_Conformal_projection) are specified. However, I find no information 
about the DATUM.  Although it is assumed to be WGS84, there is possiblity for 
data in other datum such as  Bessel-1841 specified in RT90. My question is, why 
not make the DATUM as a standard parameter? With all the effort being made by 
ncML, the inconsistency with other correctly geo-referencing dataset is still 
possible due to the lack of DATUM parameter. Am i naive or 
missing/misunderstanding something on the issue?
 
ps. some ideas about ncML and netCDF, please correct me if I am wrong
One crucial point is that the ncML is the metadata of netCDF files. Information 
in ncML is orginated from netCDF. It's true that users can edit ncML to make it 
more complete, however, it still depends on the header of netCDF.  Suppose, a 
user trying to create a data in his national coordinate system (eg. RT90) using 
CF-Conventions.  The user specified the projections and relevant parameters. It 
seems fine at first. However, when the data is distributed and people who 
download the data can't be able to know that the datum is Bessel-1841 which 
specified in RT90. The system would transfer the coordinate system using WGS84 
as datum.  That, eventually, would lead to inconsistency with other data.
 
 
Cheers
Shawn

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