Martin Hill wrote:
>
> The data modelling team are working on describing data values, which is
> useful for data servers. This forum probably needs to look at (if it's not
> done already!) how it will describe metadata in the registry using terms that
> software can interpret. How, for example, will we say that a particular data
> set contains intensities in absolute ergs, while another contains the same
> information but in magnitudes? Similarly with passband filters, pixel
> resolutions, data quality, etc, etc.
>
We very quickly get into semantics here. Obviously UNITS has to be an attribute of any measurement. Bandpasses get lots trickier because filter passbands have a shape and not just limits or a simple defining equation. In some cases, you need to know that a defined filter is used; in others, knowing the upper and lower wavelength/energy/wavenumber limits (UNITS again) is enough to decide whether the data is useful. In still other cases, knowing the wavelength category--gamma ray, xray, UV, visible, IR, sub-mm, radio, or subdivisions thereof--might be enough. Software which accesses the archive needs to be able to translate units at some level; I don't think it would be a good idea politically to require all optical data to be translated into photon energy to enter the VO when it starts out in wavelength, or vice versa for x-ray data.
-Doug Mink
Telescope Data Center
Harvard-Smithsonian Center for Astrophysics
Received on 2003-08-13Z17:58:24