Relationship between Q and STC
dsb at ast.man.ac.uk
Mon May 10 14:34:52 PDT 2004
This really and truly is the last one for today...
> > > > Because an axis is not a Quantity, it's a phenomenon.
> > >
> > > That is not true. An axis is a phenomena that describes one dimension
> > > of another phenomena. For example, "FLUX(Time)" [flux measurements
> > > recorded for a particular time] is a 1-dimensional quantity where the
> > > "TIME" quantity is both a phenomena (of "time") AND describes a
> > > dimension of (and is thus an "axis") of another.
> > The point I was making that an axis *describes* a phenomenon but does not
> > provide any values for that phenomenon. So:
> That is not true either. I may choose to store explicitly the values
> of the axis OR I may choose to use a mapping. This is an old topic
> I had thought we were past...
No - I think we just retired gasping to our corners... I still say a list
of values does not define an axis (neither does a Mapping), If I give you
[12.23, 45.3, 120.3, 1023.2]
what axis do they define? Who knows! The thing which defines the axis is
the associated metadata which says (for instance) "these numbers represent
time spent answering Q-mail, in units of minutes". This meta-data is
equivalent to a Frame. The list of numerical values (or Mapping) merely
provides some particular *values* for that axis which can be stored in
ValuesList component in the Quantity.
> Can not a phenomena be described in terms of constituent phenomena?
> This is all that is happening with STC/Q proposal. I don't believe that
> all phenomena *must* be derived from measured values. What about
> constants? Or theoretical data that I might generate? Do they not describe
> some physical phenomena as well? And since when must the Q describe
> *only* physical phenomena (??). What if I want to pass you a machine-readable
> list of numbers? The Q works well for that purpose as well..
I was using the term "measured values" in a general sense to include
anything which has an associated numerical value, as opposed to something
which does not have an associated numerical value. My point had nothing
to do with whether the values are physically measured, or predicted, or
> > Apologies! Your example made me realise that I have not been very precise
> > about what I mean by "STC". I have been equating "STC" with the
> > "CoordSystem" element. So in my previous points, make a global edit of
> > "STC"->"CoordSystem". Obviously the STC schema also includes the "Coords"
> > element which *does* include axis values, and so *is* equivalent to a
> > Quantity.
> Ah, so are we arguing then?!?
Well, yes and no. We still have different concepts of what a Quantity is,
and consequently I guess we still disagree about whether an STC
CoordSystem element is a Frame or a Quantity, but we **do** agree that
an STC Coord element is definitely a Quantity.
Dr David S. Berry (dsb at ast.man.ac.uk)
STARLINK project | Centre for Astrophysics
(http://www.starlink.ac.uk/) | University of Central Lancashire
Rutherford Appleton Laboratory | PRESTON
DIDCOT | United Kingdom
United Kingdom | PR1 2HE
OX11 0QX Tel. 01772 893733
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