Characterization draft Note

[Pierre Didelon]

Francois Bonnarel wrote:
> Dear data modellers
>    This mail to notice you that Jonathan, Mireille, Alberto, Anita, Igor
> and me have produced a draft IVOA note now available on
> http://www.ivoa.net/twiki/bin/view/IVOA/IvoaDataModel#Related_Documents
> 
>   We will take into account your comments before publishing the Note
> and are preparing the draft and implementation
> 

First of all
before any remarks, comments and complains ;-)
I really want to congratulate you for this tremendous work
with a such complete and usefull resulting document. :-)
I was no longer expecting this remembering all the discussions
and different ways open, each time a new project
oe point of view was incorporated in IVOA.

Nevertheless, ( as always!? :-( ) I have some comments
and some questions to clarify my limited understanding ;-)

# Some general remarks :

- property/axis symetry
  It is not clear if the proposed serialization has to be adopted,
if it is an example or the "actual consensus/agreement".

Until reaching the serialization, the respective points of view between
axis and property seems to be equivalent.
In such a way that confuses me a lot, it was hard for me to see
before this point, how axis information would be handle
and which is its link with properties. In other words,
it means that at least the figure 3 needs to be explain a little bit more,
mainly the CharacterisationAxis (class?) and its relation with AxisFrame.
CharacterisationAxis is derived_from/uses/... AxisFrame? ...

I was strengthen to read the  example (with <axisFrame>).
However 3.5 mention the possibility of  two (at least) different XML Schema.
I did not feel very comfortable with this.  Does it means that it will
results in characterisationByPropoerty.xsd and characterisationByAxis.xsd
different files?

- concerning Accuracy
I have a pb with the diff level and the correponding links with the frame!
If Error and ErrorBounds can clearly be related to an AxisFrame,
and so, easly included in the metadata spicifying an axis
the ErrorMap seems to be more related to the data themself
and then his relation with the axis is not so obvious.
What would be an ErrorMap for a 1D spectra, a 2D images time serie....
A small example would be welcome here p.22/23

# more specific remarks concerning the text form or details :

- concerning 2.5.2 Resolution and Sampling Precision
  I think a prelimineray remarks concerning their relations would be nice.
So a quitely different redaction like the following would perhaps be clearer,
it is only reformating except some proposed additions enclosed in []

2.5.2 Resolution and Sampling Precision
  The concepts of resolution and sampling precision (or pixelization) are related.
If the sampling precision period is small compared to the resolution, the
knowledge of a single [observed] data value is limited by the resolution [(oversampling)].
If the sampling precision period is coarse compared to the resolution, knowledge of a single
data value is limited by the sampling[(undersampling)].
  Resolution  Ultimately resolution describes
	...
	Sampling Sampling (or pixelization or precision or quantization) describes
the truncation of data values as part of the data acquisition [(]or data processing
[via re-sampling)]. If the mapping of...

- in 2.6 The layers of description
Concerning
"We generalise the four levels described for Coverage to the Resolution
and SamplingPrecision concepts."
It would be nice to have an example with eventually a figure as illustration.

- in figure 7 p.28 independantStatus doesn't appear,
even though it is mentionned in 3.2 p.20 and prisent in serialisations,
XML in 5 and VOTable in 6

Some more details, but not very important...
Enough for today perhaps ;-)
SY
PIr Didelon