[iaufwg] FITS panel recommendations; ready for review?

[Lucio Chiappetti]

On Fri, 20 Jul 2007, Don Wells wrote:

> -=-=- On escape hatches -=-=-

Thanks Don for your interesting and witty comments !

> Item 10 says XTENSION type names *must* be registered.  I would prefer a 
> strong urging accompanied by the usual justification rather than a 
> 'must', precisely because XTENSION is our most important escape hatch, 
> and I don't want to inhibit experimentation unnecessarily.  However, I 
> won't insist on this matter.

Registration seems not a very heavy task and should not hinder 
experimentation (although I did not see much experimentation in the area 
of "new extensions" but in "new conventions" or flavours of BINTABLEs. 

Maybe we should somehow formalize the registration procedure a bit more 
(de-registering if unused after an expiry time ?). In the registry 
http://fits.gsfc.nasa.gov/xtension.html I see :

 - 3 standard extensions
 - 2 conforming extensions which are just experimental precursors of
   the standard (IUEIMAGE and A3DTABLE)
 - 1 conforming extension in active use (FOREIGN)
 - 2 conforming extensions not actually implemented
 - 3 registered names never implemented

What could be the alternative ? I seem to recall that MIME allows to 
define "private" content types if their name begins with "X-" (I even 
played with my mailcap to use content types of X-FITS-image and 
X-DS9-Region to trigger ds9 via a browser).

Should we define a convention by which "experimenters" are allowed to 
define XTENSION='X-something' until they are ready to register
XTENSION='something' ? But is this really needed ? Until the unregistered 
extension is used only at one site and the file is not "widely" 
distributed, there is no harm. And even if it were distributed, I'd 
expect a generic reader to reject it with "extension 'something' 
unsupported" (after all I would not expect a *generic* reader to support
FOREIGN or A3DTABLE !).
 
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