[Fwd: Re: 20010206: netCDF Java global attributes]

• Subject: [Fwd: Re: 20010206: netCDF Java global attributes]
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Wed, 07 Feb 2001 07:48:20 -0700

-------- Original Message --------
Subject: Re: 20010206: netCDF Java global attributes
Date: Tue, 06 Feb 2001 21:44:49 -0700
From: Russ Rew <russ@xxxxxxxxxxxxxxxx>
Organization: UCAR Unidata Program
To: Winnie Cheah <winnie.cheah@xxxxxxxxxxxxx>
CC: support-netcdf@xxxxxxxxxxxxxxxx, caron@xxxxxxxx

>From: Winnie Cheah <winnie.cheah@xxxxxxxxxxxxx>
>Subject: global attributes
>Organization: ?
>Keywords: 200102070003.f1703wL21310 netCDF Java global attribute

Hi Winnie,

> This is a simply question. I want to change a global attribute value in
> an existinf netcdf file. How can I do this? The Attribute does not seem
> to have methods to do this. ... this is regarding the Java netcdf classes.

There is no way to change the value of an attribute in the Java netCDF
interface other than by copying to another netCDF file with a
different value for the attribute.  This is by design.  The
simplifications resulting from making attribute values part of the
"schema" or structural part of a netCDF file rather than part of the
"data" or changeable part of the file are considerable, and almost all
of the uses we had seen of attributes are for properties such as
"units", which don't change.  If you need to store a value that can be
changed, we recommend storing it as a variable rather than as an
attribute, since that's what variables are designed for.

If attributes can change, as in the C interface, it's necessary to
handle changing their type, size, and number of elements as well as
changing their values.  The netCDF data model seems to be simpler but
just as powerful if attributes are used to represent an extended type
for variables consisting of the immutable properties of variables.

If you have a use for redefining the value of an attribute that
wouldn't be adequately handled by using a variable instead of an
attribute, please let us know.  We might reconsider this decision.


--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
russ@xxxxxxxxxxxxxxxx                     http://www.unidata.ucar.edu