David,
On Fri, 5 Sep 2003, David Berry wrote:
> I thought I should have another bash. So I've produced a document giving
> an outline of an AST-like approach to the representation of
> transformations (i.e. Mappings - no Frames) which I intend to advertise on
> the IVOA mailing lists. It's at:
>
> http://www.ast.man.ac.uk/~dsb/ivoa/VOMapping.html
>
> I would welcome any comments (ASAP) before I make it public. Not so much
> on the detail, so much as on the overall approach. For instance, I've not
> included any formal definitions, either as XML schemas, or RDF, or
> anything else. Neither have I spent much time on the issue of how and
> where these transformations could be used within the IVOA data model.
It looks good to me, and might break the cycle of `we should think about
units', `here's some XML', `what about...'.
I think that folk _will_ ask `where's the syntax', though. The problem
is that syntax is probably the easy bit (or at least the fiddly but
uninteresting bit), and should be considered only after there's some
clarity about the thing being described. That's partly what ontologies
are for, of course, but folk do obsess about syntax, and it might be
useful to have a rejoinder up front.
The other thing is that the transformation ontology you're suggesting
here, like AST, appears more concerned with the transformation than with
the description of the coordinate system -- it could be misunderstood
as a units-conversion library. Now, that's not all that AST is, and
so it's not all that this ontology is, but, again, it might be a good
tactic to say that in words of one syllable up-front.
In the first line, you say `This document describes a proposal for the
description of transformations'. Might that be alternatively described
as `This document describes a proposal for the description of coordinate
systems', and shortly thereafter remark that a description of a coordinate
systems is equivalent to the description of the transformation from a
cartesian grid into that coordinate system, so that it reduces to the
problem which AST has addressed with great sophistication.
It might also be worth a few lines about the relationship with Arnold's
STC.
A minor thing: you quote the AST page as being on axp0.ast.man.ac.uk,
rather than www.ast..., though they appear to be currently the same
machine.
All the best,
Norman
--
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Norman Gray http://www.astro.gla.ac.uk/users/norman/
Physics and Astronomy, University of Glasgow, UK [log in to unmask]
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