[TRANSFORMS] - What is the scope of this work package?

[David Berry]

Doug,

> As we discussed in Cambridge (e.g. in the registry discussions), within the
> VO framework per-se we probably want to fix the units to one or a very few
> options, since the framework is not a user interface and we want to simplify
> the programmatic interfaces between components.  Transforming quantities
> is something that happens mainly at the boundaries of the system, e.g.,
> in the data mediators, which map external data into a data model, or in an
> application, applications framework, computational service, etc., where we
> might need to transform the data model to some application-defined model,
> or interact with the user.  These are the areas where a quantity transform
> toolkit could be most useful.  The data models will need to define the
> limited set of units permitted at the VO data model level, and might want
> to comment on the issue of transforms to and from the data model.
>
> It is not clear at this point to what extent we need transform components
> at the level of the VO data models - except for the example of WCS.  A
> good question is if we look at the data models if there are other examples
> where it is useful to define such a transform independently of a data
> object.

Without the facility to transform a Quantity from one system to another,
it is difficult to see what real use a Quantity class would be. Many
operations which you may want to perform on Quantities (such as the
example of comparison) require the values in the two Quantities to be
transformed to some common system before the operation can be
meaningfully performed.

Regarding the adoption of FITS-WCS for use within the data model, what
happens when service providers want to attach coordinates to their data
which cannot be expressed in FITS-WCS? If the IVOA data model is tied
into the FITS-WCS standard, then presumably the standard would need to be
changed to accomodate the new requirements. Given past evidence, this is
a very slow business, and could be a big barrier to such people getting
involved in the IVO.

David