Charac Answer

Doug Tody dtody at
Mon Sep 5 12:36:37 PDT 2005

It is useful to make a distinction between the type of data characterization
needed to determine if data is useful to one's analysis, and the
much more complete calibrations required to actually analyze the data.
The characterization model, at least at the higher levels, addresses the
former problem.

Even in the case of analysis the precision of the calibration information
required will vary greatly depending upon the data and the type of analysis
being performed (the time base calibration for example will vary a great
deal and much data does not require precise and rigorous time calibration).
Hence the hierarchical approach Anita describes.    - Doug

On Fri, 2 Sep 2005, Anita Richards wrote:

> > I don't think I agree.
> > The data provider should not try to second-guess the needs of the
> > client.  What that means is that the metadata accompanying a dataset
> > should be as complete as possible.  It is up to the client to decide
> > what (s)he wants to use and what not.
> Arnold, I am not saying that any meta data should not be available.  But
> very often I just want to get an image or a spectrum and to know what the
> resolution is, roughly how accurate the calibration is etc.  I will simply
> not bother if I ahve to read many pages of explanation which will
> inevitably be in jargon.  As a data provider I know very well that you
> have to offer layers.
> Providing too much information up front is extemely counterproductive,
> people think that you ahve to be an expert radio astronomer to begin to
> look at the data.  Wha is necesary is to have a heriachical apporach.  In
> my vire the Char model should just contain as much information as is
> necessary to supply a well-described data product.  If the user wants more
> information they should have a link to the Provenance or Observation or
> whatever.  Similarly, the Registry needs to know whether a particular data
> collection covres a certain bit of the sky, but retrictions on an archive
> due to the geographic location of the observatory cshould have been
> translated into sky limits for a registry entry.

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