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Re: [h5md-user] unit attributes

From: Felix Höfling
Subject: Re: [h5md-user] unit attributes
Date: Wed, 29 May 2013 12:06:06 +0200
User-agent: Opera Mail/12.15 (Linux)

Am 29.05.2013, 10:08 Uhr, schrieb Pierre de Buyl <address@hidden>:


On Mon, May 06, 2013 at 05:23:07PM +0200, Felix Höfling wrote:
Am 06.05.2013, 17:00 Uhr, schrieb Peter Colberg

>On Mon, May 06, 2013 at 04:17:57PM +0200, Felix Höfling wrote:
>>I would like to generalise and to modify the value/step/time
>>structure of data groups as
>> \-- value
>>     +-- unit
>> \-- step
>> \-- time
>>     +-- unit
>Do you have suggestions for the format of the unit attribute?
>It would be great if the unit was not some free-form text, but
>something adhering to a standard representation of SI units in
>ASCII or UTF-8. Maybe not mandatory, more as a recommendation.

Actually not, I do not make use of the unit attribute. I don't know
whether experimentalists have some standards to specify the unit
(like length is always in "metres" times a power of 10). But some
people may want to say that the unit of length is "\sigma", others
prefer Ångstrøms or cm. I think a free string would be sufficient
for the time being.

It can be left arbitrary for now. If this has to be modified in the future, it is not very complex to write tolerant parsers for this kind of corner case.

Anyway, unit can be added optionally to any dataset or attribute, from my point of view. No unit for "step" however. This could go into a general part of the
specification instead of repeating it everywhere.


Of course the "unit" attributes are always optional. But shall we change the specification and attach it to the dataset rather than the group?

In the graphical tree notation, we could indicate such fields by enclosing them in parentheses:

 \-- value
      +-- (unit)
 \-- step
 \-- time
      +-- (unit)


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