[fitsbits] SDFITS Convention Comment: Hardware Keywords

[Norman Gray]

Greetings.

On 2010 Aug 17, at 20:32, Eric Greisen wrote:

> Tom Kuiper wrote:
>> The TELESCOP keyword is required in the extension header and its 
>> associated value will be a unique string which identifies the antenna or 
>> antenna array and can be used as a key to a database of antenna 
>> parameters.  NRAO will maintain a registry for TELESCOP keyword values.
> 
> I actually like the idea of a registry - but who at NRAO did you have in 
> mind?  There was once a FITS office informally at NRAO but that 
> individual retired some years ago.  The AIPS project has been deprecated 
> for many years and depends solely on me to keep all its users afloat. 
> The CASA project has little to no interest in FITS.  The VLB users 
> maintain a registry of sorts but at a more detailed level intended to 
> represent that multiple names and abbreviations used for the same 
> telescopes when they are used in various VLBI configurations.

An alternative to a registry (or, in one view, a decentralised zeroconf registry) is to require that the TELESCOP value be a URI.

This URI should be one which the telescope, or its associated archive, publishes as the long-term 'name' of the instrument.  When retrieved, it can return either or both of human-readable and machine-readable information about the instrument and its parameters.  There are Standards-based ways of doing this.

Having said that, a URI can function perfectly happily as a _name_ for a thing, without it being required to be dereferenceable.  The DNS provides the namespacing and uniqueness guarantees.

If it's desirable (and I think it is) to have a half-way house between this decentralised approach and something more registry-like, then there'd be a very good case for using PURLs (see http://purl.org) to add a level of (curatable) indirection.  This would also help to keep the URIs within the FITS value character limit.

Best wishes,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
School of Physics and Astronomy, University of Glasgow, UK